Question

A batch of concrete is made by mixing 1 cement, 2 1/2 parts sand, and 3 1/2 parts gravel. How many pounds of sand and gravel are needed to make 300 pounds of cement? Show how you get your answer!

Answer 1

257 pounds

Explanation:

We have to assume that the "parts" are by weight. The total number of parts in a batch of concrete is 1 + 2 1/2 + 3 1/2 = 7, of which 6 are sand and gravel. The total weight of sand and gravel required for 300 lbs of concrete is ...

... (6/7)×300 lbs ≈ 257 lbs

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The actual amount is 1800/7 = 257 1/7 lbs, according to the recipe. For this sort of recipe and for this quantity, it is not unreasonable to round the answer to the nearest pound.