$A$ dishonest milkman professes to sell his milk at cost price but he mixes it with water and thereby gains $25 \%$. The percentage of water in the mixture is?

Two vessels contain milk and water in the ratio $3:2$ and $7:3$. Find the ratio in which the contents of the two vessels have to be mixed to get a new mixture in which the ratio of milk and water is $2:1$.

How much tea at $Rs. 4$ a $kg$ should be added to $15 \, kg$ of tea at $Rs. 10$ per $kg$ so that the mixture is worth $Rs. 6.50$ a $kg$? (in $kg$)

$729 \, ml$ 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 $ml$)

$A$ merchant has $1000 \ kg$ of sugar,part of which he sells at $8 \%$ profit and the rest at $18 \%$ profit. If he gains $14 \%$ on the whole,then the quantity sold at $18 \%$ profit is.......$kg$.

In what ratio must sugar at $Rs. 2$ per $kg$ be mixed with sugar at $Rs. 3.50$ per $kg$ so that the mixture is worth $Rs. 2.50$ per $kg$?