A trader buys 250 kg of onions at one price. He sells 150 kg of them at a loss of 8% and still wants a profit of 10% on the whole consignment. At what profit percent must he sell the remaining 100 kg?

Take the cost as ₹100 per kg, so the consignment costs ₹25000 and must fetch ₹27500. The 150 kg sold at 8% loss bring $150\times 92$ = ₹13800, so the last 100 kg (cost ₹10000) must fetch ₹13700 — a profit of 37%. Simply adding the shortfall to the target $(10+8=18)$ forgets that the loss was taken on 60% of the stock and must be made up on only 40% of it.