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