If $60 \%$ discount is offered on the marked price and selling price becomes equal to cost price,then what was the percentage mark up?

The banker's discount on $Rs. 2400$ at $12 \%$ p.a. is the same as the true discount on $Rs. 2520$ for the same time and at the same rate. The time is (in months):

$A$ fan is listed at $Rs. 150$ with a discount of $20 \%$. What additional discount must be offered to the customer to bring the net price to $Rs. 108$? (in $\%$)

$Rs. 20$ is the true discount on $Rs. 260$ due after a certain time. What will be the true discount on the same amount due after half of the earlier time,the rate of interest being the same? (in $Rs.$)

$A$ bill which is due at the end of $4 \text{ years}$ is now worth $Rs. 575$,but if it is due in $2 \frac{1}{2} \text{ years}$,it would now be worth $Rs. 620$. The sum of the bill is (in $Rs.$)

The present worth of a sum due after a certain time is $Rs. 1024$ and the banker's gain is $Rs. 36$. The true discount is (in $Rs.$):