The diameter of a sphere is decreased by 25%. By what per cent does its curved surface area decrease?

Explanation

Let the diameter of sphere be `d`

So, Original radius of sphere, `r=d/2`

New radius of sphere, `r^'=d/2(1-25/100)

`r^'=3/8d`

C.S.A of sphere = `4pir^2`

`4pi(d/2)^2=pid^2`

New C.S.A of a sphere = `4pir^'2`

`4pi(3d^'/8)^2=9/16pid^2`

...