If $18 \%$ of a number is $720,$ then what is $81 \%$ of the same number?

$A$ person's salary has increased from $Rs. 7200$ to $Rs. 8100$. What is the percentage increase in his salary (in $\%$)?

The price of cooking oil has increased by $15 \%$. The percentage of reduction that a family should effect in the use of cooking oil so as not to increase the expenditure on this account is:

The total population of a village is $5000$. The number of males and females increases by $10\%$ and $15\%$ respectively,and consequently,the population of the village becomes $5600$. What was the number of males in the village?

In a class of $60$ students, $40\%$ can speak only Hindi, $25\%$ can speak only English and the rest of the students can speak both the languages. How many students can speak English?

If $A = x \%$ of $y$ and $B = y \%$ of $x$,then which of the following is true?