In an exam taken by 120 students, the students who passed averaged 64 marks and those who failed averaged 28 marks. The overall average was 52. How many students passed?

Explanation

1. 01

   Passed students are $64 - 52 = 12$ above the average; failed students are $52 - 28 = 24$ below it.

2. 02

   Passed : failed = $24 : 12 = 2 : 1$.

3. 03

   Passed = $\frac{2}{3} \times 120 = 80$.