Arithmetical Operations with Significant Figures

(i) Addition and subtraction In addition and subtraction, the final

result should retain as many decimal places as there are in the number with the smallest number of decimal places.

Example:

1. 3.1 + 1.780 + 2.046 = 6.926

Here the least number of significant digits after the decimal is one. Hence the result will be 6.9.

2. 12.637 – 2.42 = 10.217

Here the least number of significant digits after the decimal is two. Hence the result will be 10.22

(ii) Multiplication and Division In multiplication or division, the final result should retain as many significant figures as there are in the original number with smallest number of significant figures.

Example:

1. 1.21 × 36.72 = 44.4312 = 44.4

Here the least number of significant digits in the measured values is three. Hence the result when rounded off to three significant digits is 44.4

2. 36.72 ÷ 1.2 = 30.6 = 31

Here the least number of significant digits in the measured values is two. Hence the result when rounded off to significant digit becomes 31.