Subject :IMO Class : Class 9
The diameter of a sphere is decreased by 25%. By what percentage its volume decreases?
A25%
B43.75%
C43.50%
D57.81%
Ans 1:
Class : Class 9
d = 75% of old d .....
=> r = 75 %of old r.....
volume of sphere =4/3 *pi*r*r*r......
new= 4/3*pi*r*r*r*27/64.....
4/3*pi*r*r*r will cancel out.....
volume(new) =27/64 of old, decreased by 37/64, % =37/64*100=3700/64=37*25/16 = 57.81....
therefore answer is opt (D) .....hope you understood!!!!!