$A$ student multiplied a number by $\frac{3}{5}$ instead of $\frac{5}{3}$. What is the percentage error in the calculation (in $\%$)?

$P$ is $20\%$ more than $Q$ and $40\%$ less than $R$. If the value of $Q$ is $₹ 150$,then what is the value of $R$ (in $₹$)?

If the side of a square is increased by $30 \%,$ its area is increased by:

One type of liquid contains $20 \%$ water and the second type of liquid contains $35 \%$ water. $A$ glass is filled with $10$ parts of the first liquid and $4$ parts of the second liquid. What is the percentage of water in the new mixture in the glass?

When the price of a product was decreased by $10 \%$,the number sold increased by $30 \%$. What was the effect on the total revenue (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?