DRDO Multi tasking staff Model paper 9

Let the weight of the student who left the class be w Kg.
Let the sum of the weight of all other students be s Kg.
Then, (s + w)/80 = 65
And, (s)/79 = 65 - 0.15 = 64.85
∴ w = - (64.85 × 79) + (65 × 80)
⇒ w = 76.85 Kg