The area of a circular ring is 352 m². If the diameter of its outer circle is 32 m, find the diameter of its inner circle.

The correct answer is: 24 m

It is given that Area of circular ring = 352 m²
Diameter of outer circle = 32 m
 Radius of outer circle,  r₁ =  =  = 16 m
Now, we know that area of the ring is difference of the areas of two circle
Let radius of outer circle be r
i.e. Area of ring = Area of outer circle – Area of inner circle
352   =  (r₁)²  -  r²
352   =  ×  (16)²  -  × (r)²
352 =  ×  (16² – r²)
112 = 256 – r²
r² = 256 – 112 = 144
r = 
r = 12
Diameter = 2  radius = 2  12 = 24 m