A trader marks up his goods by 25% over cost price and offers customers a 20% discount on the marked price. However, he uses a faulty weighing scale…

Let cost price be ₹100 per kg. Marked price = 100×1.25 = ₹125. Selling price after 20% discount = 125×0.8 = ₹100 (charged for a billed 1 kg). But the customer actually receives only 800 g, whose true cost to the trader is 100×0.8 = ₹80. Profit = SP − actual cost = 100 − 80 = ₹20 on an actual cost of ₹80, so profit% = 20/80×100 = 25%. Key idea: combine the markup/discount multiplier with the weight-cheating multiplier and compare against the ACTUAL quantity supplied, not the billed quantity.