A firm's total cost is ₹ 200 when it produces 5 units and ₹ 320 when it produces 10 units. The marginal cost per unit over this range, using MC = ΔTC/ΔQ, is:

1. MC = ΔTC / ΔQ. 2. ΔTC = 320 − 200 = ₹ 120 and ΔQ = 10 − 5 = 5 units. 3. MC = 120 / 5 = ₹ 24 per unit. 4. ₹ 120 (C) is total ΔTC not per unit, ₹ 50 (B) ignores the 5-unit jump, and ₹ 32 (D) is ATC at 10 units. Hence ₹ 24. _Source: ICAI BoS CA Foundation Paper 4 Business Economics, Ch 3 Unit II "Theory of Cost", p.6_