Alfred is buying sixty-one fluid ounces of liquid. How many cups of liquid is he buying?
Well, in the customary weights and measures system, one customary cup is equal to eight fluid ounces. Now different people around the world use the same words to mean different things. So in this question, we’re talking about US customary cups and US fluid ounces. So, we know that eight fluid ounces is equal to one cup. We want to know what sixty-one fluid ounces is equal to.
Well look, if I start off with eight fluid ounces and I divide that by eight, I’ve got an eighth as much liquid. So that’ll be one fluid ounce. Now if I took that one fluid ounce and multiplied it by sixty-one, I’d have sixty-one fluid ounces. Now let’s do the same calculation to cups. I started off with eight fluid ounces and I had an eighth as much to make one fluid ounce. So an eighth of a cup is an eighth of a cup. But I wasn’t interested in one fluid ounce; I was interested in sixty-one of them. So I need to multiply that by sixty-one.
So in cups, my measurement is an eighth times sixty-one. Well, to complete that calculation, I’m gonna turn sixty-one into its equivalent as a fraction, so sixty-one over one. Now I’ve got one over eight times sixty-one over one. And that’s sixty-one over eight. So my answer is sixty-one over eight cups. Now I could convert sixty-one over eight to a mixed number if I wanted to. And that would be seven and five-eighths cups; so either of those answers are correct.