posted by Math's Noob .
The radii of three concentric circles are 2cm, 3cm and 4cm
Find the ratio of the shaded areas A (the second circle from the inside) and B(the outer circle)
(Hint: don't substitute for pi)
A is the area between the 2-cm and the 3-cm circles
B is the area between the 3-cm and 4-cm circles.
A = pi(3^2 - 2^2) = 5pi
B = pi(4^2 - 3^2) = 7pi
B/A = 7/5