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 $L$)?

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

$A$ mixture of $48$ litre of milk and water contains $10 \%$ of water. How much water must be added to make $20 \%$ water in the new mixture?

If $5 \ kg$ of potato costing $Rs. 5$ per $kg$ and $3 \ kg$ of potato costing $Rs. 4$ per $kg$ are mixed,find the average cost of the mixture per $kg$?

Two casks of $48$ $litres$ and $42$ $litres$ are filled with mixtures of wine and water,the proportions in the two casks being respectively $13:7$ and $18:17$. If the contents of the two casks are mixed,and $20$ $litres$ of water is added to the whole,what will be the proportion of wine to water in the resultant mixture?

In a $729 \ L$ mixture of milk and water,the ratio of milk to water is $7:2.$ To get a new mixture containing milk and water in the ratio $7:3,$ the amount of water to be added is (in $L$)