In a $729 \ L$ mixture of milk and water,the ratio of milk to water is $7:2.$ To get a new mixture containing milk and water in the ratio $7:3,$ the amount of water to be added is (in $L$)

$A$ person has a chemical costing $Rs. 25$ per $litre$. In what ratio should water be mixed in the chemical so that by selling the mixture at $Rs. 20$ per $litre$,he may get a profit of $25\%$?

$A$ trader has $50 \ kg$ of sugar,a part of which he sells at $10 \%$ profit and the rest at $5 \%$ loss. He gains $7 \%$ on the whole. What is the quantity sold at $10 \%$ gain and $5 \%$ loss? (in $kg$)

In the first alloy,zinc and copper are in the ratio $1:2.$ In the second alloy,the same elements are in the ratio $2:3.$ If these two alloys are mixed to form a new alloy in which the two elements are in the ratio $5:8,$ the ratio of these two alloys in the new alloy is

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.

$A$ man has $40 \ kg$ of tea,a part of which he sells at $5 \%$ loss and the rest at the cost price. In this business,he incurs a total loss of $3 \%$. Find the quantity of tea which he sells at the cost price (in $kg$).