In what ratio must water be mixed with milk to gain $16 \%$ on selling the mixture at cost price?

In a laboratory,two bottles contain a mixture of acid and water in the ratio $2:5$ in the first bottle and $7:3$ in the second. The ratio in which the contents of these two bottles should be mixed such that the new mixture has acid and water in the ratio $2:3$ is

How much water should be added to $14$ litres of milk worth ₹ $5.40$ a litre so that the value of the mixture may be ₹ $4.20$ a litre? (in litres)

In what ratio must $25 \%$ hydrochloric acid be mixed with $60 \%$ hydrochloric acid to get a mixture of $40 \%$ hydrochloric acid?

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.

$300\, gm$ of salt solution has $40 \%$ salt in it. How much salt should be added to make it $50 \%$ in the solution? (in $gm$)