The difference between a number and its three-fifths is 50, What is the number ?

Answer: Option C

Let the number be x
Then,
$$\begin{array}{rl}& \iff x-\frac{3}{5}x=50\\ & \iff \frac{2}{5}x=50\\ & \iff x=\left(\frac{50\times 5}{2}\right)\\ & \iff x=125\end{array}$$