The way to solve this is through guess and check. 40 - 1 = 39 1 * 15 = 15 If the answer were 1, the bottle would weigh 16 pounds 40 - 2 = 38 2 * 15 = 30 If the answer were 2, then the bottle would weigh 32 pounds 40 - 2.5 = 37.5 2.5 * 15 = 37.5 The bottle itself weighs 2.5 pounds