Let cost of 1 litre milk be Re.1 Milk in 1 litre mixture in first can =

$$\frac{3}{4}litre$$

The cost price of 1 litre mixture in first can = Rs. $$\frac{3}{4}$$

In 1 litre mixture in second can = $$\frac{1}{2}litre$$

The cost price of 1 litre mixture in second can = $$Rs.\frac{1}{2}$$

In 1 litre of final mixture = $$\frac{5}{8}litre$$

The mean price = $$Rs \frac{5}{8}litre$$

By the rule of alligation we have,

$$\frac{x}{y} = \frac{(\frac{3}{4} – \frac{5}{8})}{(\frac{5}{8}- \frac{1}{2})}$$ $$\Rightarrow \frac{x}{y} = \frac{\frac{1}{8}}{\frac{1}{8}}$$ $$\Rightarrow \frac{1}{1}$$

Therefore, to get 12 litres of milk such that the ratio of water to milk is 3:5. A milk vendor should mix 6 litres of milk from each container.

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