Question

the area enclosed between the concentric circle is 770 CM square given that the radius of the outer circle is 21 CM calculate the radius of the inner circle?

Answer 1

Here,
r1=21cm and area enclosed between the concentric circle =770cm
Now,
22/7×21^2-22/7×r2^2=770cmsquare
=>22/7(21^2-r2^2)=770
=>441-r2^2=770×7/22
=>441-245=r2^2
=>196=r2^2
=>r2=14cm