$A$ mixture of $80$ litre of milk and water contains $10 \%$ water. How much water must be added to make $20 \%$ water in the new mixture? (in $litre$)

Nikita bought $30 \text{ kg}$ of wheat at the rate of $Rs. 9.50$ per $\text{kg}$ and $40 \text{ kg}$ of wheat at the rate of $Rs. 8.50$ per $\text{kg}$ and mixed them. She sold the mixture at the rate of $Rs. 8.90$ per $\text{kg}$. Her total profit or loss in the transaction was:

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?

In a bag,there are three types of coins: $1$ rupee,$50$ paise,and $25$ paise in the ratio $3:8:20$. Their total value is $Rs. 372$. The total number of coins is:

$8$ 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 water is $16:65$. How much wine did the cask hold originally? (in litres)

Some amount out of ₹$7000$ was lent at $6 \%$ $p.a.$ and the remaining at $4 \%$ $p.a.$ If the total simple interest from both the fractions in $5$ $years$ was ₹$1600$,the sum lent at $6 \%$ $p.a.$ was (in ₹).