Question 1055341
A mixture of cement, sand and gravel is in the ratio 1-2-4. Determine amounts of each needed for 1 cu. yd. of concrete. (33 1/3% voids are allowed in the sand and 45% voids allowed in the gravel).
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x + 2x + 4x = 1 cu yd
7x = 1
x = 1/7 = 0.1429  
Let x = cu. yds. of cement = 0.1429 yd
Let y = cu. yds. of sand. = 2x = 0.2857 cu yd
Let z = cu. yds. of gravel = 4x = 0.5716 cu. yd 

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Cheers,
Stan H.