If $60 \%$ of the students in a school are boys and the number of girls is $812$,how many boys are there in the school?

$15 \%$ of $578 + 22.5 \%$ of $644 = ?$

An article is sold at a discount of $20 \%$ on the marked price. In order to gain $60 \%$ on the marked price,at how much more percent of the discounted price should it be sold?

$67 \%$ of $801 - 231.17 = ? - 23 \%$ of $789$

The price of a commodity rises from $Rs. 6$ per $kg$ to $Rs. 7.50$ per $kg$. If the expenditure cannot increase,what is the percentage reduction in consumption (in $\%$)?

The population of a town was $48600$. It increased by $25\%$ in the first year and decreased by $8\%$ in the second year. What will be the population of the town at the end of $2$ years?