Example 1.4: Addition and Subtraction with Significant Figures
Rule: When we add or subtract numbers, we should round the result to the same number of decimal places as the number with the least number of decimal places (i.e., the least precise value in terms of addition and subtraction).
(a) Add
1.0023 g and
4.383 g.
(b) Subtract
421.23 g from
486 g.
Solution
\(\mathrm{sum}_{\mathrm{a}}\) \(= 1.0023\ \mathrm{g} + 4.383\ \mathrm{g}\)
\(\ \ \ =5.385\ \mathrm{g}\)
Answer is
5.385 g (round to the thousandths place; three decimal places)
\(\mathrm{diff}_{\mathrm{b}}\) \(= 486.\ \mathrm{g} - 421.23\ \mathrm{g}\)
\(\ \ \ =65.\ \mathrm{g}\)
Answer is
65 g (round to the ones place; no decimal places)