The ratio of the volumes of two empty pools is 5 : 3. If the

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BTGmoderatorAT: Moderator; Posts: 426; Joined: Tue Aug 22, 2017 8:48 pm; Followed by:1 members

The ratio of the volumes of two empty pools is 5 : 3. If the

by BTGmoderatorAT » Tue Jan 02, 2018 3:36 am

The ratio of the volumes of two empty pools is 5 : 3. If the smaller pool is filled and emptied into the larger pool, what is the ratio of filled volume to empty volume in the pools?

A. 1 : 4
B. 2 : 5
C. 3 : 5
D. 3 : 8
E. 5 : 8

I'm confused how to set up the formulas here. Can any experts help?

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Source: Beat The GMAT — Problem Solving | Tue Jan 02, 2018 3:36 am

elias.latour.apex: Master | Next Rank: 500 Posts; Posts: 228; Joined: Thu Apr 20, 2017 1:02 am; Location: Global; Thanked: 32 times; Followed by:3 members; GMAT Score:770

by elias.latour.apex » Tue Jan 02, 2018 5:43 am

You say that you have problems knowing how to set up the formulas. That is the first problem. The GMAT test is not a math test. Doing well on the test is not a matter of knowing how to generate formulas.

Every problem should be approached as though it were the first time you had seen a problem like this. To a beginner, many solutions are possible. To an expert, there are few options available and there is one, set, standard way to approach the problem. Learning default solution paths will help you reach the mid 600s, but it will never give you mastery over the test.

We start with two empty pools. Accordingly, the initial ratio of filled to empty volumes starts at 0:8. Then, we fill the smaller pool. So the filled part goes up to 3. What happens to the empty part? Does it go down or stay the same? I think we can see that it goes down. So our ratio ends up at 3:5. What happens to the ratio when the water is moved from the small pool to the large pool? Nothing. It stays 3:5.

If you're doing a lot of math, chances are you're doing something wrong.

Elias Latour
Verbal Specialist @ ApexGMAT
blog.apexgmat.com
+1 (646) 736-7622

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by [email protected] » Tue Jan 02, 2018 12:13 pm

Hi ardz24,

We're told that the ratio of the volumes of two empty pools is 5 : 3 and that the smaller pool is filled and emptied into the larger pool. We're asked for the ratio of FILLED volume to EMPTY volume in the pools. This question can be answered by TESTing VALUES.

IF....
Volume of large pool = 5
Volume of small pool = 3

Small pool is filled then emptied into the larger pool, so the large pool holds 3 and the small pool holds 0.
Total possible volume = 5+3 = 8
Current "fill" = 3+0 = 3
Current "empty" = 8 - 3 = 5
Ratio of filled to empty = 3:5

Final Answer: C

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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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

by Scott@TargetTestPrep » Mon Sep 02, 2019 6:11 pm

BTGmoderatorAT wrote:The ratio of the volumes of two empty pools is 5 : 3. If the smaller pool is filled and emptied into the larger pool, what is the ratio of filled volume to empty volume in the pools?

A. 1 : 4
B. 2 : 5
C. 3 : 5
D. 3 : 8
E. 5 : 8

I'm confused how to set up the formulas here. Can any experts help?

We can let the volume of the larger pool = 10 and the volume of the smaller pool = 6. When the smaller pool is poured into the empty larger pool, the filled volume of the pools is 6, and the empty volume of the pools is 6 + 4 = 10. Thus, the ratio of filled volume to empty volume in the pools is:

6 : 10 = 3 : 5

Alternate Solution:

Let's assume that the large pool has a volume of 5, and the small pool has a volume of 3, for a total combined volume of 8. No matter where the water is, we know that the amount of water is 3. Thus, the filled volume is 3, and the empty volume is 8 - 3 = 5, resulting in a ratio of filed : empty as 3 : 5.

Answer: C

Scott Woodbury-Stewart
Founder and CEO
[email protected]