Hi All,

We're told that a certain concrete mixture contains gravel, water, and sand in a ratio of 1 to 3 to 5 by weight. We're asked for the number of pounds of gravel that would be needed to produce 72 pounds of the mixture. This math behind this question can be approached in a number of different ways (depending on how you want to work through your calculations).

To start, a ratio of 1:3:5 means that for every 1 pound of gravel, we'll need 3 pounds of water and 5 pounds of sand. In essence, for every 1+3+5 = 9 pounds of this mixture, 1 pound of it will be gravel.

With 72 total pounds, we have 72/9 = 8 'sets' of the 1:3:5 mixture described), so we would have 8(1) = 8 pounds of gravel, 8(3) = 24 pounds of water and 8(5) = 40 pounds of sand. You'll notice that all 3 of those numbers are in the answer choices; we're asked for the number of pounds of GRAVEL though...

Final Answer: E

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