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SSC CGL 2020 PYQ — Question 8

SSC CGL Tier II - Quant - 18 Nov 2020 • Quantitative Aptitude • Q8

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If the radius of a cylinder is decreased by 20% and the height is increased by 20% to form a new cylinder, then the volume will be decreased by:

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Correct answer: A

Explanation

The correct answer is option 1 i.e. 23.2%

Let the initial radius be 'r' and height be 'h'.

Initial volume = πr2h\pi r^2h

New radius = r × .8 = .8r

New height = h × 1.2 = 1.2h

New volume = π\pi × .8r × .8r × 1.2h = 0.768πr2h\pi r^2h

% decrease = (0.232)/1 × 100 = 23.2%.