If A is 150 percent of B, then B is what percent of (A + B) ?

Answer: Option B

$$\begin{array}{rl}& A=150\%\text{ of }B\\ & \Rightarrow A=\frac{150}{100}B\\ & \Rightarrow \frac{A}{B}=\frac{3}{2}\\ & \Rightarrow \frac{A}{B}+1=\frac{3}{2}+1\\ & \Rightarrow \frac{A+B}{B}=\frac{5}{2}\\ & \Rightarrow \frac{B}{A+B}=\frac{2}{5}\end{array}$$
∴ Required percentage :
$$\begin{array}{rl}& =\left(\frac{B}{A+B}\times 100\right)\%\\ & =\left(\frac{2}{5}\times 100\right)\%\\ & =40\%\end{array}$$