SOLUTION: Dear Math Tutor, A circular ring has a cross section. if outer radius is 22mm and the inner radius is 20mm, calculate the cross sectional area of the ring. what is the cross

Algebra ->  Circles -> SOLUTION: Dear Math Tutor, A circular ring has a cross section. if outer radius is 22mm and the inner radius is 20mm, calculate the cross sectional area of the ring. what is the cross      Log On


   

Question 776744: Dear Math Tutor,
A circular ring has a cross section. if outer radius is 22mm and the inner radius is 20mm, calculate the cross sectional area of the ring.
what is the cross sectional area of a ring?
sincerely,
Nancy
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
Cut down the middle, one half of the ring may look like this:
The red circles are the places where it was cut. The diameter of those red circles is 1mm.
If by cross section they mean the area of just one of those circles, it is
pi%2A%280.5mm%29%5E2 because the are of a circle is pi%2Aradius%5E2 and the radius (half the diameter) is 0.5mm.
If by cross section they mean the area of both of those circles, it is
2pi%2A%280.5mm%29%5E2.
The approximate answers are
pi%2A%280.5mm%29%5E2=3.1416%2A0.25mm%5E2=0.7584mm%5E2 and 2pi%2A%280.5mm%29%5E2=2%2A3.1416%2A0.25mm%5E2=1.5708mm%5E2 or I would round those numbers as desired.
If an exact answer is required, I would write the results as
pi%2A%22%281%2F2+mm%29%22%5E2=pi%2A%281%2F2%29%5E2mm%5E2=pi%281%2F4%29mm%5E2=pi%2F4mm%5E2 and
2pi%2A%22%281%2F2+mm%29%22%5E2=2pi%2A%281%2F2%29%5E2mm%5E2=2pi%281%2F4%29mm%5E2=pi%2F2mm%5E2