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 ?

Answer: Option B

Let the required number of rounds be x
More radius, Less rounds (Indirect proportion)
$$\begin{array}{rl}& \therefore 20:14::70:x\\ & \iff \left(20\times x\right)=\left(14\times 70\right)\\ & \iff x=\frac{\left(14\times 70\right)}{20}\\ & \iff x=49\end{array}$$