Which number is $60 \%$ less than $80$?

Two litres of water evaporate from $10$ litres of a solution containing $10 \%$ salt. The percentage of salt in the remaining solution is

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:

If the numerator of a fraction is increased by $150 \%$ and the denominator of the fraction is increased by $300 \%$,the resultant fraction is $\frac{5}{18}$. What is the original fraction?

$A$ number is decreased by $10 \%$ and then increased by $10 \%$. The number so obtained is $10$ less than the original number. What was the original number?

There are $1400$ students in the school. $25 \%$ of them wear spectacles and $\frac{2}{7}$ of those who wear spectacles are boys. How many girls in the school wear spectacles?