The true discount on a bill of $Rs.\, 1260$ due for $6$ months at $10 \%$ per annum is (in $Rs.$):

The selling price of a radio was $Rs. 255$ when $15 \%$ discount was allowed. Then the marked price of the radio was (in $Rs.$)

$Rs.\, 20$ is the true discount on $Rs.\, 210$ due after a certain time. What will be the true discount on the same sum due after half of the former time,the rate of interest being the same? (in $Rs.$)

$A$ watch dealer pays $10 \%$ customs duty on a watch which costs $Rs.\, 500$ abroad. He desires to make a profit of $20 \%$ after giving a discount of $25 \%$ to the buyer. The marked price should be (in $Rs.$)

The marked price of a laptop is $Rs. 12000$. In a clearance sale,it is sold at a discount of $15\%$,incurring a loss of $4\%$. What is the cost price of the laptop? (in $Rs.$)

$Rs. 21$ is the true discount on $Rs. 371$ for a certain time at a certain rate of interest. If the rate of interest is kept the same,the true discount on the same sum for double that time will be (in $Rs.$)