Does deciding by totals give the same number of burgers?

The price from part (ii). Part (ii) of this question fixes the price at ₹60 a burger, and at that price, deciding one burger at a time, it finds the best choice to be 3 or 4 burgers a week. This part asks whether deciding by totals gives the same choice at the same ₹60.

Optimization by levels. Instead of looking at one more burger at a time, the consumer works out the total net benefit of every quantity, total benefit minus total spending, and picks the quantity with the largest total, as a firm does when it compares profit, total revenue minus total cost, across outputs.

Total net benefit at ₹60.

Why the answer stays the same. The largest net benefit, ₹204, is reached at 3 and at 4 burgers, exactly the quantities found at the margin in (ii). This must happen: a total is the sum of its marginal parts, so the net benefit at any quantity is the sum of the gains (marginal benefit minus price) of the burgers up to it, 120 + 60 + 24 + 0 = 204 at four. The total keeps rising while each gain is positive, stays level at the fourth burger, whose gain is zero, and falls once the gains turn negative.

Answer. Yes, the answer stays the same. By levels the net benefit is highest, ₹204, at 3 and 4 burgers, the same choice as optimization at the margin; the two methods differ only in how the comparison is set out.