Your friend drinks 2/3 of a bottle of water you drink 5/7 of a bottle of water find the difference of amounts of water left in each bottle

Well you would convert the fractions to fractions with the same denominator which would make it 14/21 for the first friend and 15/21 for the second friend. But the question is asking how much is left so you have to subtract what is left in each bottle. The first friend has 7/21 left and the second friend has 6/21 left. So, the answer is 1/21.