Question

please help me to answer no. 11 with proper steps.
Answer is (c)

Answer 1

πr^2=area

area1/area2=r^2/R^2=16:25
:.r/R=4/5

circumference=2πr
c1/c2=2πr/2πR=r/R=4/5

Answer 2

area of a circle is πr^2
circumference of a circle is 2πr
where r is the radius.
Here,
π (r1^2) / π(r2^2) = 16/25 ==> r1/r2=4/5
2 π r1 / 2 π r2 = 4/5
hence circumference is in the ratio 4:5..