Question

If the radius of a right circular cylinder open at both the ends is decreased by 25% and the height of the cylinder is increased by 25%, then the surface area of the cylinder thus formed. 

(a) Remains unaltered 

(b) Increases by 25% 

(c) Decreases by 25% 

(d) Decreases by 6.25%

Answer 1

(d) 6.25%

Original surface area = 2πrh

= \(\bigg(\frac{0.125πrh}{2πrh}\times100\bigg)\) % = 6.25%.