Question

The Chang's neighbor owns a ready-mix company. The company receives an order for 12.5 cubic yards of concrete. This mixture of concrete contains sand, cement, gravel, and water. For each pound of water, there are 5.5 pounds of sand, 2 pounds of cement, and 7.5 pounds of gravel. Determine how many pounds of cement must be used. Assume a cubic yard of concrete weighs 4,000 pounds.

Answer 1

The quantities in the proportion you give add to 16 pounds, of which 2 pounds are cement. That is, cement constitutes 1/8 of the total weight.

For each yard of concrete, 4000 lb/8 = 500 lb of cement are used.

For 12.5 yards of concrete, 12.5 * 500 = 6,250 pounds of cement will be used.

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"yard" in this case is shorthand for "cubic yard".