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The diameter of a sphere is decreased by 25%. By what percentage will its CSA be decreased?
Initial diameter = d

Initial radius = d/2

Initial S.A. = 4*Pi*(d^2)/4

New dia. = d-(25% of d)

= d-(d/4) = 3d/4

New r = 3d/8

Thus, New S.A. = 4*Pi*(9d^2)/64

Now percentage increase = [ (New S.A.)/(Initial S.A.) ] * 100

= (9/64) * 4 * 100 = 56.25 %
So, percentage decrease = 100 - 56.25 = 43.75 %


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