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
Answer
Answer (as printed): B
Explanation
Let the required number of rounds be $x$. More radius, Less rounds (Indirect Proportion). $\therefore 20:14::70:x \Leftrightarrow (20 \times x) = (14 \times 70) \Leftrightarrow x = \frac{14 \times 70}{20} \Leftrightarrow x = 49$. Hence, the required number of rounds = 49.
Explanation as extracted from the printed page; notation may be imperfect.