From a container having pure milk,$20 \%$ is replaced by water and the process is repeated thrice. At the end of the third operation,the milk is: (in $\%$ pure)

If $A$'s salary is $40\%$ less than that of $B$,then how much percent is $B$'s salary more than that of $A$?

What percentage of numbers from $1$ to $70$ have squares that end in the digit $1$?

In an examination,there are $1000$ boys and $800$ girls. $60 \%$ of boys and $40 \%$ of girls passed. The percentage of candidates that failed is: (in $\%$)

Rajiv spends $20 \%$ of his salary on food,$15 \%$ on conveyance,$10 \%$ on education,and $35 \%$ on house rent. If he spends $Rs. 1950$ on education,how much does he spend on conveyance?

The average monthly salary of all the employees in a factory is $Rs$ $8840$. If the average salary of all the officers is $Rs$ $15000$ and that of the remaining employees is $Rs$ $8000$,then what is the percentage of the officers among the employees?