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

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BTGModeratorVI: Legendary Member; Posts: 1223; Joined: Sat Feb 15, 2020 2:23 pm; Followed by:1 members

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

by BTGModeratorVI » Wed Oct 07, 2020 7:20 am

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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

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Source: Beat The GMAT — Problem Solving | Wed Oct 07, 2020 7:20 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pm; Location: Vancouver, BC; Thanked: 5254 times; Followed by:1268 members; GMAT Score:770

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

by Brent@GMATPrepNow » Sat Oct 10, 2020 7:15 am

BTGModeratorVI wrote: ↑
Wed Oct 07, 2020 7:20 am
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

Brent Hanneson - Creator of GMATPrepNow.com

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

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

by Scott@TargetTestPrep » Sat Oct 17, 2020 7:59 am

BTGModeratorVI wrote: ↑
Wed Oct 07, 2020 7:20 am
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

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