$A$ person has a chemical of ₹ $25$ per litre. In what ratio should water be mixed in that chemical,so that after selling the mixture at ₹ $20$ per litre,he may get a profit of $25 \%$?

The ratio of alcohol and water in $40$ $litres$ of mixture is $5:3$. Then $8$ $litres$ of the mixture is removed and replaced with water. Now,the ratio of the alcohol and water in the resultant mixture is

$80 \text{ litre}$ mixture of milk and water contains $10 \%$ milk. How much milk (in $\text{litre}$) must be added to make water percentage in the mixture $80 \% ?$

$A$ trader has $50 \text{ kg}$ of pulses,part of which he sells at $8 \%$ profit and the rest at $18 \%$ profit. He gains $14 \%$ on the whole. What is the quantity sold at $18 \%$ profit? (in $\text{kg}$)

In two types of brass,the ratios of Copper to Zinc are $8:3$ and $15:7$ respectively. If the two types of brass are melted and mixed in the ratio $5:2$,a new type of brass is obtained. The ratio of Copper to Zinc in this new type of brass is:

$729 \, ml$ of a mixture contains milk and water in the ratio $7:2$. How much more water is to be added to get a new mixture containing milk and water in the ratio $7:3$? (in $ml$)