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# In a 729 litres mixture of milk and water, the ratio of milk to water

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In a 729 litres mixture of milk and water, the ratio of milk to water [#permalink]
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Bunuel wrote:
In a 729 litres mixture of milk and water, the ratio of milk to water is 7:2. To get a new mixture containing milk and water in the ratio 7:3, the amount of water to be added is:

A. 51 litres

B. 61 litres

C. 71 litres

D. 81 litres

E. 83 litres

You have a solution which is 7/9th milk. You want to add water to it to get 7/10th milk.

w1/w2 = (0 - 7/10)/(7/10 - 7/9) = 9/1

So you need to add 1 ltr water for every 9 ltrs of solution. Since you have 729 ltrs of solution, you will need 81 ltr of water.

Weighted Avg and Mixtures Concepts are discussed in these posts:
https://anaprep.com/arithmetic-weighted-averages/
https://anaprep.com/arithmetic-mixtures/
and these videos:
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Re: In a 729 litres mixture of milk and water, the ratio of milk to water [#permalink]
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Re: In a 729 litres mixture of milk and water, the ratio of milk to water [#permalink]
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