Let the diameter of the sphere be d.
Radius (r1) of the sphere =d2
New radius, (r2) of the sphere =d2(1−25100)=38d
CSA (S1) of sphere =4πr21
=4π(d2)2=πd2
CSA (S2) of the sphere when radius is decreased =4πr22
=4π(3d8)2=916πd2
Decrease in the surface area of the sphere =S1−S2
=πd2−916πd2=716πd2
Percentage decrease in the surface area of the sphere =S1−S2S1×100
=7πd216πd2×100=70016=43.75%