Sara A.

asked • 02/27/16

The tire of a toy car has a diameter of 9 cm. The inner wheel has a circumference of 6 pi cm. What is the area of the tire?

A word problem of grade 9 geometry. It asks about area by giving the diameter and circumference. 

2 Answers By Expert Tutors


Kyle R. answered • 02/27/16

4.9 (31)

Mathematics and Science Tutor - Graduate Student

Kenneth S.

Using pi as given on the calculator, this area becomes 35.3429, rounded to 4 DP.
I always recommend using better than 3.14 for pi, because that's instrinsically limiting accuracy.  In the OLDEN days, 3.14 was used simply because multiplication BY HAND was arduous, but that's obsolete--why not use calculators for their inherent accuracy (in the sense of no mistakes during multiplication) and also benefit from greater accuracy of intermediate calculations.  Rounding to 2 DP, in the end, is OK by me.


Kyle R.

Yes, I agree as well, but I simplified it for the OP.  I'm assuming they are either in elementary or middle school, so I didn't feel the need to complicate it beyond the process of finding the answer.  


Kenneth S. answered • 02/27/16

4.8 (62)

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