Pure milk costs $16 / L$. After adding water,the milkman sells the mixture at $15 / L$ and thereby makes a profit of $25 \%$. In what respective ratio does he mix milk with water?

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

If $2 \, kg$ of metal,of which $\frac{1}{3}$ is zinc and the rest is copper,is mixed with $3 \, kg$ of metal,of which $\frac{1}{4}$ is zinc and the rest is copper,what is the ratio of zinc to copper in the mixture?

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.

There are $3$ tubs which contain mixtures of milk and water in the ratios of $5:2, 4:3,$ and $3:1$ respectively. If the mixtures are poured into a single tub,find the ratio of milk to water.

In an examination out of $900$ students,$85 \%$ of the boys and $70 \%$ of the girls passed. How many girls appeared in the examination,if the total pass percentage was $75 \% ?$