Solution $A$ contains $10 \%$ acid and solution $B$ contains $30 \%$ acid. In what ratio should solution $A$ be mixed with solution $B$ to obtain a mixture with $25 \%$ acid?

Nine litres of water are drawn from a container full of water and it is then filled with milk. Nine litres of mixture are drawn and the container is again filled with milk. The ratio of the quantity of water now left in the container to that of the milk in it is $16:9$. How much liquid does the container hold? (in $litres$)

$600 \, gm$ of sugar solution contains $40 \%$ sugar. How much sugar should be added to make the concentration $50 \%$ in the solution? (in $gm$)

$A$ container contains $50 \, \text{litres}$ of milk. From this container $5 \, \text{litres}$ of milk was taken out and replaced by water. This process was repeated further two times. How much milk is now contained by the container? (in $\text{litres}$)

In an examination out of $480$ students,$85 \%$ of the girls and $70 \%$ of the boys passed. How many boys appeared in the examination if the total pass percentage was $75 \% ?$

There are $65$ students in a class. $39$ rupees are distributed among them so that each boy gets $80$ Paise and each girl gets $30$ Paise. Find the number of boys and girls in that class.