GMATinsight wrote: ↑

Tue Jul 21, 2020 7:54 am

A milkman mixes some water in 10 liters of 90% pure milk solution and obtains an 80% pure milk solution. Find the quantity of water he added.

A) 0.75 liter
B) 1 liter
C) 1.25 liters
D) 1.5 liters
E) 2.25 liters

Source: www.GMATinsight.com

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Let's try as follows:

In \(10\) litres of \(90\%\) mixture, \(9\) liters is milk and water will be \(1\) liter.

As we are not adding any more milk, \(9\) liters must be \(80\%\) of the resultant solution.

\(9=\dfrac{80}{100}\cdot x \Longrightarrow x=11.25\).

As there are \(10\) liters already, an additional \(1.25\) liters of water to be added.

Therefore, C