At what percent above the cost price must a person mark the price of an article so that he can enjoy $20 \%$ profit after allowing $20 \%$ discount?

$Rs. 21$ 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 $Rs.$)

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

The marked price of an article is $20 \%$ more than its cost price. If $5 \%$ discount is given on the marked price,what is the profit percent (in $\%$)?

If on a marked price,the difference between the selling prices with a single discount of $30 \%$ and two successive discounts of $20 \%$ and $10 \%$ is $Rs.\, 72$,then the marked price (in $rupees$) is:

If the simple interest on $Rs. 2000$ at $5\%$ $p.a.$ is equal to the true discount on $Rs. 2500$ for the same time and at the same rate,the time is (in $years$)