SSC GD 18th Feb 2019 Shift-3

Question 63

If the radius of a sphere is decreased by 25%, then the percentage decrease in its surface area is:

Solution

Surface area of a sphere=$$4\pi r^{2}$$=X
r1=0.75r
Surface area of new sphere=$$4\pi (0.75r)^{2}$$
=9/16 (Y)
Percentage decrease in the area=((Y-(9/16)Y)/Y)*100
=900/16
=43.75%


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