$A$ trader marks the sale price $25\%$ more than the cost price and gives a $10\%$ discount at the time of selling. The gain percent is (in $\%$)

Find the present worth of a bill of $Rs.\, 3720$ which is due for $2\, years$ at $12 \%$ compound interest,being compounded annually. (in $Rs.$)

If the true discount on $Rs. 161$ due for $2$ years and $6$ months is $Rs. 21$, then find the rate of interest (in $\%$).

If $Rs. 21$ is the true discount on $Rs. 371$ for a certain time,what is the true discount on the same amount for double that time,the rate being the same in both the cases? (in $Rs.$)

The present worth of a certain sum due sometime hence is $Rs. 1700$ and the true discount is $Rs. 170$. The banker's gain is (in $Rs.$)

$A$ book seller allowed $10 \%$ discount on the printed price. He gets a $30 \%$ commission from the publisher. His profit percentage will be: