In what proportion must water be added to spirit to gain $20 \%$ by selling it at the cost price (in $:5$)?

How much water must be added to a vessel which contains $80$ litres of milk at a cost price of ₹ $3.5/litre$ so that the cost of the milk reduces to ₹ $2/litre$? (in litres)

The average monthly salary of employees,consisting of officers and workers of an organization,is ₹$3000$. The average salary of an officer is ₹$10000$ while that of a worker is ₹$2000$ per month. If there are a total of $400$ employees in the organization,find out the number of officers and workers separately.

$8$ litres are drawn from a cask full of wine and is then filled with water. This operation is performed three more times. The ratio of the quantity of wine now left in the cask to that of the water is $16$:$65$. How much wine did the cask hold originally? (in litres)

How many $kg$ of salt at $42$ $P$ per $kg$ must a man mix with $25 \, kg$ of salt at $24$ $P$ per $kg$,so that he may,on selling the mixture at $40$ $P$ per $kg$,gain $25 \%$ on the outlay?

$A$ 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?