Mixtures: Milk and Water

Question

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

Night reader · Answer

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

Anurag@Gurome · Answer

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)

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GMATGuruNY · Answer

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/
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RadiumBall · Answer

Wow perfect OA: B

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