Significant figures are the digits in a number that represent the precision of a measurement. They are important in scientific calculations because they indicate the level of uncertainty in a measurement and help ensure the accuracy of the final result.
The rules for determining significant figures are as follows:
1) All non-zero digits are significant
2) Zeros between non-zero digits are significant
3) Zeros before the first non-zero digit are not significant
4) Zeros at the end of a number after a decimal point are significant
5) Zeros at the end of a number before a decimal point may or may not be significant, depending on the measurement tool and the context of the calculation.
The number 0.5 is significant because it represents a measured value with one decimal place of precision. It should be included as a significant figure in the final result.
The final answer should have the same number of significant figures as the measurement with the fewest significant figures in the calculation. In this case, 0.5 has only one significant figure, so the final answer should also have one significant figure.
The correct way to express the answer is 100, since 0.5 times 234.987 is equal to 117.4935, which should be rounded to one significant figure.