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

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