$25 \%$ of $25 \% = ?$

$A$ man spends $15 \%$ of his income. If his expenditure is $Rs$ $75,$ his income (in rupees) is:

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

If $25 \%$ of a number is subtracted from a second number,the second number reduces to its $5/6$. What is the ratio of the first number to the second number?

What percent of Rs. $2650$ is Rs. $1987.50$?

After giving a $25 \%$ discount on the entry ticket,the number of visitors increased by $30 \%$. What will be the impact on the total revenue from entry tickets compared to other days?