1. (3) Several students left the lyceum and several came. As a result, the number of students decreased by $10 \%$, and the share of boys in the lyceum increased from $50 \%$ to $55 \%$. Did the number of boys increase or decrease?
## 1. Answer: Decreased.

Let there initially be $n$ students in the lyceum. Then at first there were $n / 2$ boys, and then $-n \cdot 0.9 \cdot 0.55=n \cdot 0.495$.