Mutiplication and Division with Sginificant Figures

The rule for multiplication and division is similar to that for addition and subtraction, but uses significant figures instead of decimal places. 

Specifically, you count the number of significant figures in each number in the original problem. The answer will have the same number of significant figures as the smallest number of significant figures in the problem.

For example, 20.663*32.1=663 (this is 663.2823 rounded to 3 significant figures). 

Two more examples: 

30.1*0.00334552 = 0.101

38*4.771=180

These rules often produce answers that seem wrong, but they are the correct way to deal with measurements.

Keep in mind that when you need to “trim” a calculator answer down to follow these rules that if the digit after the last number being kept is 0-4 we do NOT change the number. If the digit following the last “kept” number is 5-9 we round up. In other words 3.642 rounded to the second decimal place is 3.64, while 3.647 rounded to the second decimal place is 3.65.

Addition and Subtraction Problems with Decimal Places

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