SOLUTION: The density and strength of concrete are determined by the ratio of cement and aggregate. Suppose that a contractor has 480ft^3 of a dry concrete mixture that is 70% sand by volume

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Question 897072: The density and strength of concrete are determined by the ratio of cement and aggregate. Suppose that a contractor has 480ft^3 of a dry concrete mixture that is 70% sand by volume. How much pure sand must be added to form a new mixture that is 75% sand by volume?
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
Available, 480 cubic feet concrete mix at 70% sand.

A mixture is wanted which is 75% sand. How much sand to add to the available material?

Let s = volume of sand to add.

highlight_green%28%28480%2A70%2Bs%29%2F%28480%2Bs%29=75%29
Solve for s.