Question

The radius of a solid right circular cylinder decreases by 20% and its height increases by 10%. Find the percentage change in its : curved surface area.

Answer 1

Curved surface area (Original) of a solid right circular cylinder = 2πrh

= 2π × 100 × 100

= 20000π cm² 

Curved surface area (New) of a solid right circular cylinder 

= 2πr'h'

= 2π × 80 × 110

= 17600π cm² 

Decrease in curved area

= Original CSA – New CSA

= (20000π – 17600π) cm²

= 2400π cm² 

Percentage change in curved surface area = `"Decrease in curved surface area"/"Original curved surface area" xx 100%`

= `(2400 pi  cm^2)/(20000 pi  cm^2) xx 100%` 

= 12%