question_answer

A right circular cone is enveloping a right circular cylinder that rests on the base of the cone. If the radius and the height of the cone is 4 cm and 10 cm respectively, the radius of the cylinder is ?r? cm and the largest possible curved surface area of the cylinder is \[\text{ }\!\!'\!\!\text{  }\!\!\pi\!\!\text{ }\,\,\text{ar(b-r) }\!\!'\!\!\text{ ,}\] then \[a\times b=?\]

A)  15                               

B)  20    

C)  21                               

D)  24