Question

The diameter of a sphere is decrease by 20%by what percent does its C.S.A is decrease?

Answer 1

let initial diameter of sphere=100 unit
now ,
cross section area =pi.r^2=pi. (d/2)^2
=pi.d^2/4=10000/4.pi square unit
when decrease diameter 20%
then diameter of sphere =100-20=80 unit
now C.S.A =pi. (80)^2/4
=6400 pi./4
now
change in CSA=3600pi/4
hence % change in CSA=(3600pi/4)/(10000pi/4) x 100
=36 %