A. 5

B. 10

C. 20

D. 30

### Solution(By Apex Team)

Let the initial number of persons be x. Then, $\begin{array}{l}\text{⇒ 16x + 20 × 15 = 15.5 (x + 20)}\\ \text{⇒ 0.5x = 10}\\ \text{⇒ x = 20}\end{array}$