A hostel mess feeds 35 students. When 7 more students join, the total daily expense rises by ₹840, but the average daily expense per student falls by ₹4. What was the original total daily expense of the mess?

Explanation

1. 01

   Let the original average be ₹x per student, so the original total is 35x.

2. 02

   New total = $42(x - 4) = 35x + 840$.

3. 03

   $42x - 168 = 35x + 840$, so $7x = 1{,}008$ and $x = 144$.

4. 04

   Original total = $35 \times 144$ = ₹5,040.