A toothed wheel of diameter 50 cm is attached to a smaller wheel of diameter 30 cm. How many revolutions will the smaller wheel make the larger one makes 15 revolutions ?

Answer: Option C

Distance covered by smaller wheel in 1 revolution :
$$\begin{array}{rl}& =\left(2\pi \times 15\right)cm\\ & =\left(30\pi \right)cm\end{array}$$
Distance covered by larger wheel in 1 revolution :
$$\begin{array}{rl}& =\left(2\pi \times 25\right)cm\\ & =\left(50\pi \right)cm\end{array}$$
Let,
$$k\times 30\pi =15\times 50\pi$$
Then,
$$k=\left(\frac{15\times 50\pi }{30\pi }\right)=25$$
∴ Required number of revolution = 25