###
**How many litres of water should be added to a 30 litre mixture of milk and water containing milk and water in the ratio of 7 : 3 such that the resultant mixture has 40% water in it?**

A. 5
B. 2
C. 3
D. 8
**Answer: Option A**

## Show Answer

Solution(By Apex Team)

Total quantity of mixture
$\begin{array}{l}
=\frac{7}{7+3} \times 30 \text { litres }\\
=21 \text { litres }
\end{array}$
And quantity of water in the mixture
$\begin{array}{l}
=\frac{3}{7+3} \times 30 \text { litres }\\
=9 \text { litres }
\end{array}$
Let water to be mixed ‘a’ litre
Then,
$\begin{aligned}&\Rightarrow(30+a)\times\frac{40}{100}=9+a\\
&\Rightarrow120+4a=90+10a\\
&\Rightarrow120-90=10a-4a\\
&\Rightarrow30=6a\\
&\Rightarrow a=5\end{aligned}$
Hence, 5 litres water mixed in the mixture.

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