Significant Figures Rules for Addition and Subtraction

What is the answer rounding with significant figures?

I thought it would be 9.5 since 21 has two significant figures but it’s not.

948 or 9.48 x 10^2

Answer:

The correct answer rounding with significant figures is 948 or 9.48 x 10^2.

When dealing with significant figures, there are different rules for addition and subtraction compared to multiplication and division. In this problem, the numbers involved are 78.9, 890.43, and -21.

For addition and subtraction, the rule is that the number of decimal places in the answer must not exceed the number of decimal places in the least precise number.

In this case, the number -21 has the fewest digits after the decimal point (none). Therefore, the answer must also have no digits after the decimal point. Hence, the correct answer is 948, with three significant figures, or 9.48 x 10^2.