Three sections have 30, 40 and 50 students. The first section averages 72 marks and the second averages 66. The overall average of all 120 students is 64. What is the average of the third section?

Explanation

1. 01

   Overall total = $120 \times 64 = 7{,}680$.

2. 02

   First two sections total = $30 \times 72 + 40 \times 66 = 2{,}160 + 2{,}640 = 4{,}800$.

3. 03

   Third section total = $7{,}680 - 4{,}800 = 2{,}880$.

4. 04

   Average = $\frac{2880}{50} = 57.6$.