Question 1203899
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The ratio of sand to gravel in the first pile is 1:3, which means 1/4 is sand and 3/4 is gravel.  24 cubic feet are taken from this pile; the amount of sand in those 24 cubic feet is 1/4 of 24 cubic feet, which is 6 cubic feet.<br>
The ratio of sand to gravel in the second pile is 3:5, which means 3/8 is sand and 5/8 is gravel.  40 cubic feet are taken from this pile; the amount of sand in those 40 cubic feet is 3/8 of 40 cubic feet, which is 15 cubic feet.<br>
ANSWER: The amount of sand in the mixture is 6+15 = 21 cubic feet.<br>