What is the rate of interest when the $P.W.$ of $Rs. 1245$ due in $15$ months is $Rs. 1200$? (in $\%$)

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

The present worth of $Rs. 220.50$ due in $2$ years reckoning compound interest at $5 \%$ per annum is (in $Rs.$):

$Rs. 20$ 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 $Rs.$)

The banker's gain on a certain sum of money due for $9$ months at $4 \%$ $p.a.$ is $Rs. 2.25$. The sum is (in $Rs.$)

Find the present worth $(P.W.)$ and the true discount $(T.D.)$ reckoning $6 \%$ per annum simple interest of $Rs. 176$ due in $20 \text{ months}$ time. (in $Rs.$)