Question: A mixture of 40 litres of milk and water, contains 20% of water. How much water must be added to the mixture to make the water 25% of the new mixture?

1. 2 l
2. 7/3 l
3. 8/3 l
4. 3 l
5. 4 l

Correct Answer: (C)
Solution and Explanation:
Approach Solution 1:

The problem statement informs that:

Given:

• A mixture of 40 litres of milk and water contains 20% of water.

Find Out:

• Amount of water to be added to the mixture to make the water 25% of the new mixture.

The total amount of mixture = 40 litres
Amount of water in mixture = 20/100 ∗40
= 8 litre

Let the amount of water added to make the concentration of water 25% be x litre

Therefore, the new amount of solution = 40 + x litre,
Therefore, the amount of water in the new solution = 8 + x litre

Hence we can say, 8 + x = 25/100 (40 + x)

That can be derived as 32 + 4x = 40 + x
Or, 3x = 40 – 32 = 8
Therefore, x = 8/3 litre

Hence, the amount of water added to make the concentration of water 25% is 8/3 litre.

Approach Solution 2:

The problem statement states that:

Given:

• There is a mixture of 40 litres of milk and water
• The mixture contains 20% of water.

Find Out:

• Amount of water to be added to the mixture to make the water 25% of the new mixture.

Impure milk : Water = 75 : 5 = 15 : 1

Therefore, the amount of water to be added to the mixture to make the water 25% of the new mixture = 40/15 x 1 = 8/3 litres.

Approach Solution 3:

The problem statement suggests that:

Given:

• There is a mixture of 40 litres of milk and water
• The mixture contains 20% of water.

Find Out:

• Amount of water to be added to the mixture to make the water 25% of the new mixture.

Quantity of water in the mixture = 20% of 40 ltrs = 8 ltrs

Therefore, the addition of water to make it 25% of the new mixture can be written as:
(8+x)/(40+x) = ¼
Therefore, x= 8/3
Hence, the amount of water to be added to the mixture to make the water 25% of the new mixture = 8/3 litres

“A mixture of 40 litres of milk and water, contains 20% of water”- is a topic of the GMAT Quantitative reasoning section of the GMAT exam. This question has been taken from the book “Foundations of GMAT Math”. GMAT Problem Solving questions test the analytical skill and calculative efficiency of the candidates to solve quantitative problems. GMAT Quant practice papers include various types of questions that allow the candidates to improve their mathematical learning.

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