A hotel has 459 managers. When the number of managers is increased by 36, the total daily expenditure on food increases by ₹81, but the average food expenditure per person decreases by ₹1. Find the hotel’s original daily expenditure on food.

Let the expense be "X" for 459 managers , and let per head expense on food be "y" initially :
459(Y) = X .... Equation I

Now as increasing managers to 459+36 = 495 managers & it is said that per head expense is decreased by 1 now, so per head expense now would be "Y-1" . And it is also said that upon increasing managers, the expenses got increased by 81 , Hence total expense would be "X+81" :

495 (Y-1) = X + 81.... Equation 2

Upon solving both equations we arrive at Y = 16 & X = 7344.

Therefore, the original spending on food is Y = 7344.