In a $120$ $litre$ mixture of milk and water,water is only $25 \%$. The milkman sold $20$ $litre$ of this mixture and then added $16.2$ $litre$ of pure milk and $3.8$ $litre$ of pure water to the remaining mixture. What is the percentage of water in the final mixture (in $\%$)?

$A$ person travels $285 \text{ km}$ in $6 \text{ hours}$ in two stages. In the first part of the journey,he travels by bus at a speed of $40 \text{ km/h}$. In the second part of the journey,he travels by train at a speed of $55 \text{ km/h}$. How much distance did he travel by train? (in $\text{km}$)

Two casks of $48$ $litres$ and $42$ $litres$ are filled with mixtures of wine and water,the proportions in the two casks being respectively $13:7$ and $18:17$. If the contents of the two casks are mixed,and $20$ $litres$ of water is added to the whole,what will be the proportion of wine to water in the resultant mixture?

Zinc and copper are in the ratio $5:3$ in $400 \, g$ of an alloy. How much copper (in $g$) should be added to make the ratio $5:4$?

In a mixture of $75 \, litres$,the ratio of milk to water is $2:1$. The amount of water to be further added to the mixture so as to make the ratio of milk to water $1:2$ will be (in $litres$):

The average weekly salary per head of all employees (supervisors and labourers) is ₹ $100$. The average weekly salary per head of all the supervisors is ₹ $600$,while the average weekly salary per head of all the labourers is ₹ $75$. Find out the number of supervisors in the factory if there are $840$ labourers in it.