In a class of $80$ students,each student got sweets that are $15 \%$ of the total number of students. How many sweets were there?

Two-fifths of one-third of three-seventh of a number is $15$. What is $40$ per cent of that number?

If $40 \%$ of a number is equal to two-third of another number,what is the ratio of the first number to the second number?

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?

The population of a city is $20000$. It increased by $20\%$ during the first year and $30\%$ during the second year. The population after two years will be:

In an office,$40 \%$ of the staff is female,$70 \%$ of the female staff and $50 \%$ of the male staff are married. The percentage of the unmarried staff in the office is