The ratio of milk and water in $66$ $litres$ of adulterated milk is $5:1$. Water is added to it to make the ratio $5:3$. The quantity of water added is (in $litres$):

$100$ $litres$ of a mixture contains $20 \%$ water and the rest is milk. The amount of milk that must be added so that the resulting mixture contains $87.5 \%$ milk is (in $litres$):

In a mixture of milk and water of volume $30 \ L$,the ratio of water and milk is $3:7$. How much quantity of water should be added to the mixture to make the ratio of milk and water $1:2$ (in $L$)?

$A$ person covers a distance of $100\, km$ in $10\, hours$,partly by walking at $7\, km/h$ and the rest by running at $12\, km/h$. Find out the distance covered in each part (in $km$).

If $2 \, kg$ of metal,of which $\frac{1}{3}$ is zinc and the rest is copper,is mixed with $3 \, kg$ of metal,of which $\frac{1}{4}$ is zinc and the rest is copper,what is the ratio of zinc to copper in the mixture?

$A$ can contains a mixture of two liquids $A$ and $B$ in the ratio $7:5$. When $9\,L$ of mixture is drained off and the can is filled with $B$,the ratio of $A$ and $B$ becomes $7:9$. How many litres of liquid $A$ was contained by the can initially?