### 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

### 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.

## Related Questions On Alligation

A. 2 : 5
B. 3 : 5
C. 5 : 3
D. 5 : 2

### An alloy contains zinc, copper and tin in the ratio 2 : 3 : 1 and another contains copper, tin and lead in the ratio 5 : 4 : 3. If equal weights of both alloys are melted together to form a third alloy, then the weight of lead per kg in new alloy will be:

A. $\large\frac{1}{2} \mathrm{~kg}$
B. $\large\frac{1}{8} \mathrm{~kg}$
C. $\large\frac{3}{14} \mathrm{~kg}$
D. $\large\frac{7}{9} \mathrm{~kg}$

A. 81 litres
B. 71 litres
C. 56 litres
D. 50 litres