Question

$. = 383835565 { = 30 \times \frac{?}{?} }^{?}$

Answer 1

Area of outer circle=πr^2
=22/7 multiply 21x21
=66x21=1386cm square
area enclosed between circles =770 cm square
so area of inner circle =1386-770=616 cm square
area of inner circle =πr^2=22/7 multiply r^2
616x7/22=r^2
4312/22=r^2
392/2=r^2
196=r^2
r=14 cm