There were 35 students in a hostel. Due to the admission of 7 new students the expenses of the mess were increased by Rs.42 per day while the average expenditure per head diminished by Re 1. What was the original expenditure of the mess?

Explanation:-

Let the original average expenditure be Rs.x then, 42(x - 1) - 35x = 42.
=> 7x = 84
=> x = 12
Therefore original expenditure,
= Rs.(35 * 12)=Rs.420.