$A$ 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?

Three glasses of capacity $2 \, L$,$5 \, L$,and $9 \, L$ contain mixtures of milk and water with milk concentrations of $90 \%$,$80 \%$,and $70 \%$ respectively. The contents of the three glasses are emptied into a large vessel. Find the ratio of milk to water in the resultant mixture.

$A$ mixture of milk and water measures $60 \, ltr$. It contains $20 \%$ water. How many litres of water should be added to it so that water may be $25 \% $ (in $ltr$)?

Pencils at $Rs. 4.20$ per dozen are mixed with pencils at $Rs. 5.40$ per dozen in the ratio $3:5$. Find the price per dozen of the mixture (in $Rs.$).

$A$ $20\, \text{litre}$ mixture of milk and water contains milk and water in the ratio $3:2$. $10\, \text{litres}$ of the mixture is removed and replaced with pure milk,and the operation is repeated once more. At the end of the two removals and replacements,what is the ratio of milk and water in the resultant mixture?

In a bag,there are three types of coins: $1$ rupee,$50$ paise,and $25$ paise in the ratio $3:8:20$. Their total value is $Rs. 372$. The total number of coins is: