When 12 marbles are added to a rectangular aquarium, the water in the aquarium rises 1 1/2 inches. In total, how many marbles must be added to the aquarium to raise the water 2 3/4 inches?

Answer:21 marbles would be added to raise the water 2 3/4 inches

Step-by-step explanation:

When 12 marbles are added to a rectangular aquarium, the water in the aquarium rises 1 1/2 inches. Converting 1 1/2 inches to improper fraction, it becomes 3/2 inches

Let x represent the number of marbles that would be added to the aquarium to raise the water 2 3/4 inches. Converting 2 3/4 inches to improper fraction, it becomes 11/4 inches. Therefore

12 marbles = 3/2 inches rise

x marbles = 11/4 inches rise

Cross multiplying,

12 * 11/4 = 3/2 * x

33 = 3x/2

3x = 33 * 2 = 66

x = 66/3 = 21