1. **Stating the problem:** The total number of students in a school is 1650. 70% of the pupils are boys. We need to find how many girls are there in the school. 2. **Formula and explanation:** To find the number of girls, we first find the number of boys using the percentage given, then subtract from the total number of students. Number of boys = 70% of total students = $0.70 \times 1650$ Number of girls = Total students - Number of boys 3. **Calculations:** Number of boys = $0.70 \times 1650 = 1155$ Number of girls = $1650 - 1155 = 495$ 4. **Answer:** There are 495 girls in the school.