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?

Question

anonymous · Answer

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

anonymous · Answer

Still a little confused..

whpalmer4 · Answer

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.