Tips & Tricks Now, cost price of 100 g is Rs. 100 But instead of 100 g he sells 80 g at the price of 100 g So, 80 g is sold at Rs. 100 Actual cost price of 80 g = Rs. 80 Actual selling price of 80 g = Rs. 100 Profit = [(selling price – cost price)/cost price] × 100 ⇒ profit = [(100 - 80)/80]× 100 = (20/80) × 100 = 25% Short Trick: Profit% = [(true weight - false weight)/false weight] × 100 ⇒ profit% = [(100-80)/80] × 100 = 25%