Question 0.5: A Calculation Using Significant Figures It takes 9.25 hours ......
A Calculation Using Significant Figures
It takes 9.25 hours to fly from London, England, to Chicago, Illinois, a distance of 3952 miles. What is the average speed of the airplane in miles per hour?
First, set up an equation dividing the number of miles flown by the number of hours:
\text { Average speed }=\frac{3952 \ \mathrm{mi}}{9.25 \mathrm{~h}}=427.24324 \ \mathrm{mi} / \mathrm{h}Next, decide how many significant figures should be in your answer. Because the problem involves a division, and because one of the quantities you started with (9.25 h) has only three signifcant figures, the answer must also have three signifcant figures. Finally, round of your answer. The first digit to be dropped (2) is less than 5, so the answer 427.243 24 must be rounded of to 427 mi/h.
In doing this or any other problem, use all figures for the calculation, whether signifcant or not, and then round of the final answer. Don’t round of at any intermediate step.