When 12 marbles are added to a rectangular aquarium, the water

[BTGModeratorVI]

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?

A. 16
B. 18
C. 20
D. 22
E. 24

Answer: D
Source: Magoosh

[Brent@GMATPrepNow]

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?

A. 16
B. 18
C. 20
D. 22
E. 24

Answer: D
Source: Magoosh

We can solve this question using equivalent ratios

We'll use the ratio: #of marbles/rise (in inches)

Let x = the number of marbles required to raise the water 2 3/4 inches (aka 2.75 inches).

We can write: 12/1.5 = x/2.75

Cross multiply to get: (1.5)(x) = (12)(2.75)
Simplify: 1.5x = 33
Solve: x = 33/1.5 = 22

Answer: D

Cheers,
Brent

[Scott@TargetTestPrep]

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?

A. 16
B. 18
C. 20
D. 22
E. 24

Answer: D

Solution:

We can create the proportion:

12/(3/2) = x/(11/4)

24/3 = 4x/11

24(11) = 12x

2(11) = x

22 = x

Alternate Solution:

We observe that the addition of each marble raises the water (1 1/2)/12 = (3/2)/12 = 1/8 inch. Thus, to raise the water 2 3/4 = 11/4 inches, we need (11/4)/(1/8) = (11/4) x (8/1) = 11 x 2 = 22 marbles.

Answer: D

[gentvenus]

I've lost my marbles on this one