Question 218851
 A 2:3 concrete mix means that for every two parts of sand , three parts of gravel are used. How much sand should be used in a mix composed of 25 cubic feet of gravel?
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2:3 is the same as 2x:3x where 2x is the sand and 3x is the gravel.
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Equation:
2x + 3x = 25 ft^3
5x = 25 
x = 5 ft^3
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sand = 2x = 10 ft^3
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Cheers,
Stan H.