Given: A shopkeeper sells two at Rs. 5,000 each. He gains 20% on one and loses 20% on another. Formula Used: Gain% = (selling price - cost price)/cost price × 100; loss% = (cost price - selling price)/cost price × 100 Calculation: ⇒ cost price of first item, when it is sold at 20% gain = 5000/1.20 = Rs. (50000/12) ⇒ cost price of second item, when it is sold at 20% loss = 5000/0.80 = Rs. 6250 ⇒ cost price of both items = Rs. (6250 + 50000/12) ⇒ selling price of both items = Rs. (5000 + 5000) = Rs. 10000 ⇒ overall loss% = (6250 + 50000/12 - 10000)/(6250 + 50000/12) × 100 ⇒ 416.66/10166.66 × 100 ⇒ 4% ∴ required loss = 4% When two items of same selling price, sold at a% loss and a% gain, then there is always loss occur in the overall transaction which is same as (a)2/100% so overall loss% = (20 × 20/100)% = 4%