Question

The size of a bicycle is determined by the diameter of the wheel. You want a 21-in bicycle for your birthday. What is the area of one of the wheels?

Answer 1

2r = 21 -> r = 21/2, put that in the area formula

Answer 2

Still a little confused..

Answer 3

First, the size of a bicycle is not determined by the diameter of the wheel. Bicycles come in all sorts of different sizes with constant wheel sizes. But no matter...

Area of a circle is given by \[A=\pi r^2\] or \[A=\frac{\pi d^2}4\] depending on whether you know the radius \(r\) or the diameter \(d\). The diameter is what you know in this case.