The diameter of a sphere is decreased by 25%

Let Diameter=d, radius of sphere=rs=d/2
New radius=d/2(1-25/100)=3d/8=rn
Curved Surface Area=4πrs²=4π(d/2)²=πd²
Curved Surface Area (when radius decreased)=4πrn²=4π(3d/8)²=9/16πd²
Decrease=πd²-9/16πd²=7/16πd²