If the height of a cylinder is increased by 15 per cent

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If the height of a cylinder is increased by 15 per cent and the radius of its base is decreased by 10 per cent then by what percent will its curved surface area change?

1. 3.5 per cent decrease
2. 3.5 per cent increase
3. 5 per cent increase
4. 5 per cent decrease

Per cent change in surface area

=		x + y +	xy
			100

=		15 + (-10) +	15 × (-10)
			100

=		15 - 10 -	150		= [15 - 11.5]
			100

= 3.5 per cent.
(+ve) sign shows 3.5 per cent increases.