A coaching batch of 45 students averaged 64 marks in a mock test. The boys averaged 60 and the girls averaged 69. How many girls are in the batch?

Explanation

1. 01

   Boys : girls = $(69 - 64) : (64 - 60) = 5 : 4$.

2. 02

   Total parts = 9, so 1 part = $45 \div 9 = 5$ students.

3. 03

   Girls = $4 \times 5 = 20$.