The circumference of two circles are in the ratio 2 : 3. Find the ratio of their areas.
Let r1 and r2 be the radii of two given circles and C1 and C2 be their circumference.
Then, C1:C2=2:3
⇒2πr1:2πr2=2:3
⇒r1:r2=2:3
⇒r21:r22=4:9
⇒πr21:πr22=4:9
Hence, ratio of areas is 4:9.