Milk and water in a mixture are in the ratio $7:5$. When $15 \, L$ of water is added to it,the ratio of milk and water in the new mixture becomes $7:8$. The total quantity of water in the new mixture is........$L$

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

Three glasses of equal volume contain acid mixed with water. The ratios of acid to water are $2:3$,$3:4$,and $4:5$ respectively. If the contents of these glasses are poured into a large vessel,what is the ratio of acid to water in the large vessel?

In what ratio must water be added to spirit to gain $10 \%$ by selling it at the cost price?

Haresh earned ₹ $4000$ per month. From the last month,his income increased by $8\%$. Due to a rise in prices,his expenditure also increased by $12\%$ and his savings decreased by $4\%$. Find his increased expenditure and initial savings.

$A$ 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?