A ticket costs ₹200 for an adult and ₹120 for a child. A group of 10 can spend at most ₹1,700. At least how many of them must be children?

Explanation

1. 01

   With $c$ children: $200(10 - c) + 120c \le 1{,}700$, so $2{,}000 - 80c \le 1{,}700$.

2. 02

   $80c \ge 300$, so $c \ge 3.75$: at least 4 children.