Quantitative Aptitude Ques 1137

Question: If the height of a cylinder is increased by 15% and the radius of its base is decrease by 10%, then by what per cent will its curved surface areas change?

Options:

A) 3.5% decrease

B) 3.5% increase

C) 5% increase

D) 5% decrease

Show Answer

Answer:

Correct Answer: B

Solution:

  • Let height of cylinder be h and radius be r. Then, curved surface area $ =2\pi rh $ Now, height $ (h’)=h+\frac{15}{100}h=\frac{23h}{20} $ and radius $ (r’)=r-\frac{10}{100}r=\frac{9r}{10} $ Now, curved surface area $ =2\pi r’h’ $ $ =2\pi ( \frac{9r}{10} )( \frac{23h}{20} )=2\pi \frac{(207),rh}{200} $ Change in curved surface area $ =( \frac{2\pi \times \frac{207rh}{200}-2\pi rh}{2\pi rh} )\times 100 $ $ =\frac{7}{200},\times $ =3.5% increase
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