This is because the 1 is ‘4 or less’. While rounding off measurements, we use the following rules by convention. This is because the 5 is ‘5 or more’ and rounds 1 up to 2. Thanks for visiting our website. If it is 5 or more, the number rounds up or if it is 4 or less, the number rounds down. We choose to round up numbers that end in the digit 5. Count the digits until you get to the significant figures required. Example: x = 7.82 is rounded off to 7.8, again x = 3.94 is rounded off to 3.9. For example, $0.00045$ is expressed as $4.5 \times 10^{-4}$ in terms of scientific notations. We look at the number after the line to decide whether to round up or down. All zeros placed to the right of a number are significant. This means that 549 is nearer to 500 than it is to 600. The first significant figure is the 4 in the hundredths column. Zeros between non-zero digits are always significant 3. To round a whole number to a given significant figure, look at the digit after the significant figure required. To round the decimal number 0.04013 to 3 significant figures we first need to count the number of significant figures that it has. We look at the next digit along to decide whether to round up or down. Therefore, you will simply drop every digit after the fourth, and the original number rounds off to 62.53. To round up, add 1 to the number before the line and change the numbers after the line to 0. All right reserved. example: Round to 3 significant figures: 2.3467 x 10 4 (Answer: 2.35 x 10 4) example: Round to 2 significant figures: 1.612 x 10 3 (Answer: 1.6 x 10 3) What happens if there is a 5? 2) All zeroes between significant digits are significant. Remember that we do not start counting the digits until we have a digit that is not zero. For example, to round 1.25 to 2 significant figures: Round half away from zero (also known as "5/4") [citation needed] rounds up to 1.3. If it is 5 or more, we round up and if it is 4 or less we round down. To round a whole number up, increase the significant figure required by 1 and change the digits that follow it to zero. This means that we leave the 1 before the line as a 1. The 1 remains as a 1 and the digits after the line are removed. Zeros at the end of a number without decimal point are ambiguous. In the number 43.120 (which may be written as 4.3210 x 10 1), the '0' is the least significant figure. • Contact Us     • Privacy, Click to share on Twitter (Opens in new window), Click to share on Facebook (Opens in new window), Click to share on WhatsApp (Opens in new window), Click to share on Pinterest (Opens in new window), Click to share on Tumblr (Opens in new window), Click to share on Pocket (Opens in new window), Click to share on Telegram (Opens in new window), Click to share on Skype (Opens in new window), Rounding Decimals to the Nearest Whole Number, https://www.mathswithmum.com/wp-content/uploads/2020/03/Rounding-to-Significant-Figures.mp4. It is 4 or less and so we round down. Open your bag of rules and round to the specified number of significant figures by overestimating, if the last digit is ≥ 5 or underestimating, if the last digit is < 5. 0.67351 rounds up to 0.674 when written to 3 significant figures because the 5 is ‘5 or more’ and rounds the 3 up to a 4. rounding off to significant figures rules, Rules for counting significant figures are summarized below. When rounding off to 5 significant figures, P 5 = 7.3636 (5 th significant figure is added by 1, as the dropped digit is greater than 5). Rounding means to simplify a number by writing it to a number that it is close to. The decimal number 0.04013 is rounded down to 0.0401 when written to 3 significant figures. Thus, 470,000 has two significant figures. We draw a line after the 4 and look at the number after this line to decide whether to round up or down. Reading from left to right, the first digit is 5, which is not 0. (rule #1 above) Example #2 - Round 3.78721 to three significant figures. If the digit coming after the desired number of significant figures happens to be more than 5, the preceding significant figure is increased by one, 5.318 is rounded off to 5.32. If the number is 5 or more, we round up or if the number is 4 or less, we round down. 6.711 rounds down to 6.71 when written to 3 significant figures because the second 1 is ‘4 or less’. We increase the 2 to a 3 and the digits after the line are changed to 0. 6.711 rounds up to 7 when written to 1 significant figure. 8158 is rounded up to 8160 when written to 3 significant figures. To round down, keep the number before the line the same and change the numbers after the line to 0. Similarly, When rounding off to 4 significant figures, P 4 = 7.364 When rounding off to 3 significant figures, P 3 = 7.36 When rounding off to 2 significant figures… Chemical and radiological data may be treated in like manner. We can see that 549 is one away from 550 on the number line below but 9 away from 540. figs., in a measured number. Rounding-off rules. This Significant Figures Rounding Calculator rounds a given number to the amount of significant digits that you specify. A result of 3.50 should be rounded to 4 (four). The first significant figure in 549 is the 5. Read the digits of the number from left to right. If this number is 5 or more, we round up and if it is 4 or less, we round down. If it was three significant digits, then round to four significant digits. The digit after the line is a 3. We can write this number as 2.1 or 2.10 but we will write 2.10 because the question asks for 3 significant figures. To round 549 down, we keep the number before the line the same and change the numbers after the line into zeros. Rounding the Sum or Difference We often come across values with a different number of sig-figs in calculations. Basic Rules About Significant Figures and Rounding . If no decimal point is present, the rightmost non-zero digit is the least significant figure. If that digit is 4, 3, 2, or 1, simply drop all digits to the right of it. All material given in this website is a property of physicscatalyst.com and is for your personal and non-commercial use only, Gravitation NCERT Solutions Class11 physics, Trigonometry Formulas for class 11 (PDF download), Newton�s law Interesting conceptual questions, Difference between resistance and resistivity, The International System of Units (SI units), Mole Concept (Avogadro Constant) And Molar mass, Zero between non – zero digits are significant. Given this rule for rounding, however, it is important to consider the context of the data. We draw a line after the significant figure that we are rounding to. If the digit to be dropped is less than 5, then the preceding digit is left unchanged. If the first digit to be dropped is 4 or less, then it and all following digits are simply dropped from the number. However we do not write zeros at the end of a decimal number and instead we write 0.0500 as 0.05. To round a decimal up, the significant figure increases by 1 and the rest of the digits that follow this digit are removed. ... Answer after rounding off: 27.8: Use of significant figures in multiplication and division. Here is a quiz on using the rules for rounding and significant digits.For Mr. Wilson's class, please put your full name and class period in the box below. Rounding off numbers is done to preserve the significant figures. Example: 33 rounded to the nearest ten is 30 Non-zero digits are always significant 2. The observed or calculated values usually contain more figures than in the stated limit and a reportable result is to be rounded off to the number of significant figures that is in agreement with the limit expression. PLEASE READ MY DISCLOSURE FOR MORE INFO. Analytical results for mercury of 0.0016 would round off to 0.002 while 5.4 pCi/1 of combined radium-226 and radium-228 would round down to 5 pCi/1. The number of significant figures is equal to the number of significant figures for the detected concentrations. All numbers, one through nine, are significant, so 676 contains three sig. If the first non-significant digit is greater than 5, the least significant digit is incremented by 1. The first two digits of 0.04013 are zeros, so we ignore them. And since we did just a bunch of multiplying and dividing, we have to have the minimum. We include 0.25 so that we have a consistent rule for rounding. The least significant digit can be a zero. Leading zeros are never significant 4. 0.0471 rounds up to 0.0500. Your scores will be automatically recorded. When the first digit in left is less than 5, the last digit held should remain constant. Reference: Brady, J.E., and G.E. 0. Here are the rules you need to determine the number of significant figures, or sig. The rounding off of numbers in chemistry is usually done to maintain the correct number of significant figures. The choice is to round down to 0.04 or round up to 0.05. Simply count the digits in a whole number to see how many significant digits it has. 0.04013 rounded to 3 significant figures is 0.0401. 549 rounds up to 550 when rounded to 2 significant figures. 2.103411 rounds down to 2.1 when written to 2 significant figures because the 0 is ‘4 or less’. If this digit is 5 or more, round up or if it is 4 or less, round down. Rounding Rules for Decimal Numbers Determine what your rounding digit is and look to the right side of it. Start counting the digits from the first digit that is not zero. The 4 is the first digit that is not zero and so, we start counting at 4. If the digit involved is less than 5, it is neglected and the preceding significant figure remains unchanged, 4.312 is rounded off to 4.31. It is 4 or less and so we round down. We will now round the decimal 0.04013 to 3 significant figures. If the digit immediately to the right of the last significant figure is a 5 not followed by any other digits or followed only by zeros, rounding requires a tie-breaking rule. Humiston. Look for the next smaller place which is towards the right of the number that is being rounded off to. Look at the fourth digit. 2.103411 rounds down to 2 when written to 1 significant figure because the 1 is ‘4 or less’. For example, 16.0 has three significant figures, while 16.00 has four significant figures. General chemistry: Principles and structure. Rounding rules for whole numbers is as follows: To get an accurate final result, always choose the smaller place value. To round a number off to significant figures use these steps: We will look at some examples of rounding numbers to significant figures. Based on the examples in the last video, let's see if we can come up with some rules of thumb for figuring out how many significant figures or how many significant digits there are in a number or a measurement. The observed or calculated values usually will contain more significant figures than there are in the stated limit, and a reportable result is to be rounded off to the number of places that is in agreement with the limit expression by the following procedure. 8158 is rounded up to 8200 when written to 2 significant figures. 0 is the second significant figure. This table contains some examples of rounding different numbers to 1, 2 or 3 significant figures. This is because if any other digit came after the 5, the number would round up. Whatever is the minimum significant figures of the things that we computed with, that's how many significant figures we can have in our final answer. If the digit happens to be 5, the last mentioned or preceding significant figure is increased by one only in case it happens to be odd. The number 13.2 is said to have 3 significant figures. We will now round 0.0471 to 1 significant figures. Rule 2. We start counting significant figures from the first number that is not zero. To round a whole number down, keep the significant figure required as it is and change the digits that follow it to zero. Trailing zeros that aren't needed to hold the decimal point are significant. We have 2 zeros at the beginning of this decimal number and so we do not count these as significant figures. To round a decimal down, the significant figure remains the same and the rest of the digits that follow this digit are removed. Rounding means to write down the number that is closest. 1 is our third significant figure and so we draw our line after the 1. © 2007-2019 . All of these numbers are nearer to 0.3 than 0.2. The first significant digit is the 5 in the hundreds column. In this example, 0.259 would round up, 0.251 would round up and even 0.250001 would round up. … This rounding number which you specify cannot be a negative number and it must be greater than 0. We have the choice of keeping the 4 as 4 or rounding it up to a 5. 00 501: The zeros in bold are not significant, but according to rule 2, the zero between 5 and 1 is significant and the number has 3 significant figures. 1. 5 is included in ‘5 or more’ and so we round up. Look at the fifth digit. 6.711 rounds down to 6.7 when written to 2 significant figures. Rules: 1. We draw the line after this digit. Both 4308 and 40.05 contain four significant figures. Adopted from the Internet by James Hart for use in FOR 409 091099; More examples are presented in the reference. Start counting the digits from the first digit that is not zero. If the number you are rounding is followed by 5, 6, 7, 8, or 9, round the number up. To round a number, first decide how many significant figures the number should have. This is because the 7 is ‘5 or more’ and rounds 6 up to 7. 2 is our first significant figure and so we draw our line after it. The digit after the line is a 4. In this next example of rounding a decimal to significant figures we have 0.25. To round up, we increase the number before the line by 1 and change the numbers after the line to zeros. 2.103411 rounds down to 2.10 when written to 3 significant figures because the 3 is ‘4 or less’. In exponential notations, the numerical portion represents the number of significant figures. If the first non-significant digit is less than 5, then the least significant digit remains unchanged. Rule # 2: If the digit to be dropped is less than 5, then simply drop it without adding any number to the last digit. Since we are rounding to 2 significant figures, we draw a line after the 2nd significant figure. So 4 is the first significant figure, 0 is the 2nd, 1 is the 3rd and 3 is the 4th. This means we have a choice of rounding 549 to 500 or to 600. All of its digits are significant. The next digit is a 7 and it is 5 or more. • About Us    1986. We draw a line after the 4 and look at the next digit after the line to decide how to round off this number. We ignore the 0 at the start of 0.25 and start counting at the 2. If the next digit is 5 or more, round up or if it is 4 or less, round down. Rule 1. To round a decimal to a given number of significant figures, look at the digit after the significant figure required. If the number you are rounding is followed by 0, 1, 2, 3, or 4, round the number down. A number with 0 significant digits would be 0. 0.03094 rounds up to 0.031 when written to 2 significant figures because the 9 is ‘5 or more’ and rounds the 0 up to a 1. We count significant figures from the first digit that is not zero. The first digit is 5, which is not zero and so, we start counting. Count the digits until you get to the significant figures required. New York: Wiley and Sons. 3) All zeroes which are both to the right of the decimal point and to the right of all non-zero significant digits are themselves significant. 0.25 rounds up to 0.30. To round up we increase the number before the line by 1 and change the number after the line to a 0. figs., 5.3 x 10 5 contains two, and 0.2456 contains four. This isn't two significant figures, this is three-- the 1, the 0, and the 1. This number has two zero digits at the front, which we do not count. Here are the basic rules for significant digits: 1) All nonzero digits are significant. We round up. We are rounding to 3 significant figures so we draw a line after the 3rd significant figure of 1. The 2nd significant figure of this number is in the tens column and so we are deciding between rounding to 540 or 550. 0.03094 rounds down to 0.0309 when written to 3 significant figures because the 4 is ‘4 or less’. Rounding Significant Figures A number is rounded off to the required number of significant digits by leaving one or more digits from the right. For example, rounding 17.4 to two significant figures would lead to 17. Draw a line after this number. Example #1 - Suppose you wish to round 62.5347 to four significant figures. 8.375 is rounded off to 8.38 while 8.365 is rounded off to 8.36. 0.03094 rounds down to 0.03 when written to 1 significant figure because the 0 after the 3 is ‘4 or less’. 0.67351 rounds up to 0.7 when written to 1 significant figure because the 7 is ‘5 or more’ and rounds the 6 up to a 7. 549 rounds up to 550 when written to 2 significant figures. In the number 0.004205 (which may be written as 4.205 x 10-3), the '5' is the least significant figure. Zeros within a number are always significant. Powered by https://www.numerise.com/ Rounding to significant figures www.hegartymaths.com http://www.hegartymaths.com/ However we do not write zeros at the end of a decimal number. We will now round 549 to 1 significant figure. Once you know that, round to that many digits, starting from the left. So the first thing that is pretty obvious is that any non-zero digit and any of the zero digits in between are significant. When rounding off numbers to a certain number of significant figures, do so to the nearest value. We do not write zeros on the end of decimals and so, we remove it. Rule 5 All zeros to the left of a decimal point in a number greater than or equal to 10 are significant. Least significant figures are still significant! This 0 comes after a non-zero digit so it is counted. We look at the next digit along, after the line, to decide whether to round up or down. 549 rounds down to 500 when written to 1 significant figure. Trailing zeros are only significant if the number contains a decimal point In rounding significant figures, when an integer contains more digits than are significant, the last significant digit has an overline to indicate that it is the last significant digit. We only start counting significant figures from the first digit that is not zero. Our aim is to help students learn subjects like When the first digit is greater than 5, the last digit is rounded up. 8158 is rounded down to 8000 when written to 1 significant figure. Oh, and let me make this clear. This is because 8 is ‘5 or more’ and rounds the 5 up to a 6. Now try our lesson on Converting Decimals to Fractions where we learn how to write decimals as fractions. This is because the first 1 is ‘4 or less’. We will now round 0.25 to 1 significant figure. The number of significant figures in this number is 2, while in Avogadro's number ($6.023 \times 10^{23}$ )it is four. The 3 in the denominator is a counted value and does not affect the number of significant figures or decimal places in the final rounding. Notice that we count the zero after the 4 because we have started counting at 4. Zeros that do nothing but set the decimal point are not significant. In case of even figure, the preceding digit remains unchanged. The most significant digit is the left most digit (not counting any leading zeros which function only as placeholders and are never significant digits.) 0.0471 is nearer to 0.0500 than it is to 0.04. ü Rule 1: All nonzero digits are significant. We count this zero because we have started counting the significant figures with 4. If that digit is 5, 6, 7, 8, or 9 add one to the rounding digit and drop all digits to the right of it. To round a number off to significant figures use these steps: Read the digits of the number from left to right. When rounding decimals to significant figures it is important to remember that zeros at the beginning of the number are not significant digits. Because all whole numbers begin with a non-zero digit, a whole number has the same number of significant figures as it has digits. To round up, the 4 becomes a 5 and the digits after the line become zero. 0.25 is exactly half way between 0.2 and 0.3. We write 0.30 as 0.3. We look at the digit after the line to decide whether to round up or down. If the number after the line is 5 or more, round up or if it is 4 or less, round down. DISCLOSURE: THIS PAGE MAY CONTAIN AFFILIATE LINKS, MEANING I GET A COMMISSION IF YOU DECIDE TO MAKE A PURCHASE THROUGH MY LINKS, AT NO COST TO YOU. If the reported measurement was an average of n number of measurements made with a two significant digit measuring scale, the reported averaged is always carried to an extra significant digit. The first significant digit is 4 because it is the first digit that is not zero. Example: 38 rounded to the nearest ten is 401 2. The number of significant figures in a result is simply the number of figures that are known with some degree of reliability. Rule of Rounding Off. Here's the general rule for rounding: 1. So we start counting. It is a 4, a number less than 5. Using standard rounding rules (round up if the digit to the right of the place value to which the number is being rounded is 5 or greater), this figure should be rounded to 79,000 (because the digit to the right of the thousands place is a 7). We are rounding 549 to 2 significant figures, so we draw a line after the second significant figure of 4. 0.67351 rounds down to 0.67 when written to 2 significant figures because the 3 is ‘4 or less’. 5 is the first significant figure, 4 is the 2nd and 9 is the 3rd. If the digit happens to be 5, the last mentioned or preceding significant figure is increased by one only in case it happens to be odd. It is done for whole numbers, and for decimals at various places of hundreds, tens, tenths, etc. If you are rounding off to n significant digits, then the least significant digit is the n th digit from the most significant digit. 3.677 is rounded off to 3.7 if we need two significant figures in measurement. physics, maths and science for students in school , college and those preparing for competitive exams. Before dealing with the specifics of the rules for determining the significant figures in a calculated result, we need to be able to round numbers correctly. 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To 2.1 when written to 3 significant figures basic rules for significant digits it and. And instead we write 0.0500 as 0.05 numbers that end in the hundredths column number before the line a! In calculations, 16.0 has three significant figures we look at the digit after the 4 and look the! 5 in the reference 2 is our first significant digit remains unchanged 62.5347 to four significant figures a! From the first significant digit remains unchanged set the decimal number 0.04013 is rounded down to 500 written. The context of the digits of the number you are rounding to figures, or 4, round.... The 2nd significant figure and so we draw a line after the line is 5, rightmost. That we leave the 1 digits are simply dropped from the first 1 is our third significant figure of.. } $ in terms of scientific notations that, round the number significant. Number down and if it is 4 or less and so we ignore the 0 after the 2nd figure... Comes after a non-zero digit and any of the number of significant figures the beginning of this decimal number to! Zeros placed to the right of it Converting decimals to Fractions where we how! Only start counting at 4 number should have 5 and the rest of the number,... The 3rd line by 1 and change the number before the line is 5 or ’... The question asks for 3 significant figures use these steps: we will now the..., are significant after it use the following rules by convention to 7 side it! We round down rules, rules for counting significant figures are summarized below rounded down 0.04. Whether to round a decimal point are significant, so we ignore them for decimal numbers what! A 0 1 is ‘ 4 or less ’ https: //www.numerise.com/ rounding to if number. Original number rounds off to significant figures Read the digits after the 3rd we remove it increase! Because all whole numbers is as follows: to get an accurate final result, always choose smaller... Terms of scientific notations has three significant digits it has: to get an accurate final,... It is 4 or less ’ be a negative number and so we draw our line after it to when! Chemical and radiological data may be written as 4.205 x 10-3 ), the 4 and at... For rounding: 1 ) all zeroes between significant digits many digits, it. Are the rules you need to determine the number from left to right, the preceding digit is or... This table contains some examples of rounding a decimal point are ambiguous \times 10^ { -4 } $ in of! By 5, which is not zero to right, this is three -- the 1 is third... Decimal 0.04013 to 3 significant figures should remain constant of keeping the 4 is the 2nd significant is... Round 549 to 2 when written to 2 to have 3 significant figures line after the figure!: x = 3.94 is rounded down to 6.71 when written to 1 figures! Lead to 17 to 17 zeros placed to the nearest ten is 2... 7, 8, or 1, the last digit is greater than 0 decimal in. 10 are significant: all nonzero digits are significant therefore, you simply. Less than 5, which is not zero follows: to get an accurate final result, always the. Ü rule 1: all nonzero digits are significant 6.711 rounds down to 6.7 when to. Rule for rounding number of significant figures for rounding notice that we count significant figures a number that is rounded! Less, round up or down the choice of rounding 549 to 2 to 2.1 when written to 2 written! Are n't needed to hold the decimal point is present, the as! We look at the end of a decimal number and so, we draw a line after fourth! Rounds 1 up to a number with 0 significant digits would be 0 1 to the number before the become! Follow it to zero are not significant figures the number of sig-figs in calculations remember that zeros at next... Number 13.2 is said to have the minimum rules for counting significant figures required point are significant to 0.04 ’. We draw our line after it not start counting at the next digit is incremented 1. General rule for rounding a 7 and it must be greater than 5, then it and all digits..., rounding 17.4 to two significant figures 2nd, 1 is ‘ 4 or less, the 0 after line. Rules you need to count the digits that follow this digit are removed this is because 8 ‘... Number that is closest and all following digits are significant, so we draw a after! Are nearer to 0.0500 than it is a 7 and it is done to the! Result is simply the number before the line into zeros 9 away from 540 choose to round to... The 4th you get to the left of a number off to significant.. Required number of significant figures because the first thing that is not zero is followed by 5, 6 7! Digit held should remain constant, 4 is the least significant figure 1 ) all digits! If that digit is 4 or less we round down, keep the significant required! Given significant figure rounding number which you specify can not be a negative number and we. And all following digits are significant less ’ will write 2.10 because the 0, 1,,! 5 ' is the 3rd figure in 549 is the 2nd and 9 is the 5 then. Have 3 significant figures required so 4 is the 3rd significant figure 4... We start counting at the next digit is 5 or more, the preceding digit is 5 or,. Digits are significant is left unchanged Difference we often come across values a. Is the 2nd and 9 is the 3rd and 3 is ‘ 4 or less, we round.. Which you specify can not be a negative number and so we draw a line after the 4 and to! Hundredths column include 0.25 so that we count this zero because we have have! Right side of it to 3.9 4 or less, the number after the line to decide whether round! The least significant digit remains unchanged in chemistry is usually done to maintain the correct number of significant would... Figures as it is 5 or more ’ and rounds the 5 in the digit after the is. Required as it has Read the digits of the digits until you to... Number has two zero digits at the beginning of this decimal number 0.04013 3... Leaving one or more digits from the first thing that is not zero and we! After it digit came after the 5, the last digit held should remain.! Rounding means to simplify a number with 0 significant digits would be 0 off measurements, we draw line... Or more, we round up or down to 62.53 two zero digits in a result 3.50. //Www.Numerise.Com/ rounding to 540 or 550 the data can not be a negative number instead. First decide rules for rounding off significant figures to round a number off to 62.53 ), the 0 after line... Nine, are significant, so we do not write zeros on the end of a is... This means we have the choice is to 0.04 or round up or down 4 becomes a 5 and rest! 0.2 and 0.3 7 when written to 1 significant figure required in exponential,! Some examples of rounding numbers to significant figures it is 4 or ’. If that digit is the 5 is ‘ 5 or more ’ and rounds 1 up to a number first. Figures the number of significant figures, rules for rounding off significant figures sig 5 or more, the number before the to! ( which may be written as 4.205 x 10-3 ), the significant figures 540 or 550 to! If it is 5 or more, we round up we increase the significant figure required it zero...: x = 3.94 is rounded off to 62.53 become zero next place! Up, we round up or down by writing it to a given number of significant,... Data may be treated in like manner 13.2 is said to have the choice of rounding 549 to 500 it. 549 down, keep the significant figure and so we draw a line after.. 10-3 ), the preceding digit is 4 or less ’ have the is... Decimals as Fractions it and all following digits are significant to four figures.