Two numbers are respectively 20% and 50% of the third number. What percent is the first number of the second ?

Answer: Option D

Let the 3^rd number is 100
According to the question,
$$\begin{array}{rl}& 1^{\text{st}}{2}^{\text{nd}}{3}^{\text{rd}}\\ & 20:50:100\end{array}$$
Required % = $$\frac{20}{50}$$ × 100 = 40%