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1. A rope makes 70 rounds of the circumference of a cylinder whose radius of the base is 14 cm. How many times can it go round a cylinder with radius 20 cm ?

A. 40

B. 49

C. 100

D. None of these

Solution:

Let the required number of rounds be x
More radius, Less rounds (Indirect proportion)

\begin{aligned} ∴ 20 : 14 :: 70 : x \\ \Leftrightarrow (20 \times x) = (14 \times 70) \\ \Leftrightarrow x = \frac{(14 \times 70)}{20} \\ \Leftrightarrow x = 49 \end{aligned}

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