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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.
Solution
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%
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