There were 35 students in a hostel. Due to the admission of 7 new students, ;he expenses of the mess were increased by Rs. 42 per day while the average expenditure per head diminished by Rs 1. What was the original expenditure of the mess? Choose the correct choice from the following:
A) 320  B) 120  C) 400  D) 420  E) 514

Rationale: "sol . let the original average expenditure be rs . x . then , 42 ( x - 1 ) - 35 x = 42  7 x = 84  x = 12 . original expenditure = rs . ( 35 x 12 ) = rs . 420 . . answer d"
Answer: D