$A$ sum of ₹ $390$ was divided among $450$ boys and girls. Each girl gets $50$ paise and each boy gets one rupee. How many girls are there among them?

$A$ bottle contains $81$ litres of pure milk. $\frac{1}{3}$ of the milk is replaced by the same amount of water. Again,$\frac{1}{3}$ of the mixture is replaced by the same amount of water. The ratio of the milk and water in the new mixture is

In a mixture of milk and water of volume $30 \ L$,the ratio of water and milk is $3:7$. How much quantity of water should be added to the mixture to make the ratio of milk and water $1:2$ (in $L$)?

$A$ drum contains $80$ $litres$ of ethanol. $20$ $litres$ of this liquid is removed and replaced with water. $20$ $litres$ of this mixture is again removed and replaced with water. How much water (in $litres$) is present in this drum now?

$80 \text{ litre}$ mixture of milk and water contains $10 \%$ milk. How much milk (in $\text{litre}$) must be added to make water percentage in the mixture $80 \% ?$

Three bottles of equal capacity contain mixtures of milk and water in the ratios $2:5$,$3:4$,and $4:5$ respectively. These three bottles are emptied into a large bottle. What will be the ratio of milk and water respectively in the large bottle?