Mixtures: Milk and Water

Expert replies

RadiumBall: Master | Next Rank: 500 Posts; Posts: 132; Joined: Thu Dec 02, 2010 2:49 am; Thanked: 5 times

by RadiumBall » Sun Mar 13, 2011 5:45 pm

In 60 litres of a milk solution the concentration of water is 20%. When some quantity of pure milk is added to this, the concentration of milk changes to 90%. What is the total quantity of milk solution formed?
A) 96 litres
B) 120 litres
C) 114 litres
D) 108 litres
E) 54 litres

Like this post

Source: Beat The GMAT — Problem Solving | Sun Mar 13, 2011 5:45 pm

Night reader: Legendary Member; Posts: 1337; Joined: Sat Dec 27, 2008 6:29 pmFollowed by: 10 members; Thanked: 127 times

by Night reader » Sun Mar 13, 2011 6:05 pm

the answer to this problem is 120 litres choice B

By using alligation method, we take pure milk's concentration of the second solution %%(100-90)=10 and assign this rate to 80% concentration of milk. We do the same with the 80% concentrated solution and assign %%(90-80)=10 to pure milk. Next we take the ratio of the final quantity received after mixing of two solutions, name this as X and divide it by %%(10+10) numbers Only. Here (X/20)*10=60 OR X=120 liters

for more explanation about alligation method please see this post https://www.beatthegmat.com/those-of-you ... 71770.html

RadiumBall wrote:In 60 litres of a milk solution the concentration of water is 20%. When some quantity of pure milk is added to this, the concentration of milk changes to 90%. What is the total quantity of milk solution formed?
A) 96 litres
B) 120 litres
C) 114 litres
D) 108 litres
E) 54 litres

My knowledge frontiers came to evolve the GMATPill's methods - the credited study means to boost the Verbal competence. I really like their videos, especially for RC, CR and SC. You do check their study methods at https://www.gmatpill.com

Like this post

GMAT/MBA Expert

Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Sun Mar 13, 2011 6:41 pm

RadiumBall wrote:In 60 litres of a milk solution the concentration of water is 20%. When some quantity of pure milk is added to this, the concentration of milk changes to 90%. What is the total quantity of milk solution formed?
A) 96 litres
B) 120 litres
C) 114 litres
D) 108 litres
E) 54 litres

Solution:
Let the quantity of pure milk added be 'x'.
Now, initially, the quantity of pure milk in 60 liters of milk solution was (80/100) * 60 = 48 liters.
After adding x liters, new quantity of pure milk is 48+x liters.
Also, new quantity of milk with water is 60+x liters.
So, (48+x)/(60+x) = 90/100 = 9/10.
Or, 480+10x = 540+9x.
Or x = 60 liters.
Hence, total quantity of milk solution formed is 60+60 = 120 liters.

Anurag Mairal, Ph.D., MBA
GMAT Expert, Admissions and Career Guidance
Gurome, Inc.
1-800-566-4043 (USA)

Join Our Facebook Groups
GMAT with Gurome
https://www.facebook.com/groups/272466352793633/
Admissions with Gurome
https://www.facebook.com/groups/461459690536574/
Career Advising with Gurome
https://www.facebook.com/groups/360435787349781/

Like this post

GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Sun Mar 13, 2011 7:16 pm

RadiumBall wrote:In 60 litres of a milk solution the concentration of water is 20%. When some quantity of pure milk is added to this, the concentration of milk changes to 90%. What is the total quantity of milk solution formed?
A) 96 litres
B) 120 litres
C) 114 litres
D) 108 litres
E) 54 litres

Almost no math is needed here.

The original solution is 20% water.
The added milk is 0% water.
Since the percentage of water in the final solution -- 10% -- is halfway between 20% and 0%, the final solution must contain equal amounts of the original solution and the added milk.

Thus, added milk = 60 liters, and the total volume = 60+60 = 120 liters.

The correct answer is B.

Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3

Like this post

RadiumBall: Master | Next Rank: 500 Posts; Posts: 132; Joined: Thu Dec 02, 2010 2:49 am; Thanked: 5 times

by RadiumBall » Sun Mar 13, 2011 8:39 pm

Wow perfect OA: B

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

559 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review