The true discount on a certain bill due for nine months at $4 \%$ simple interest is $Rs.\, 150$. Find the amount of the bill (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 $Rs.$)

Successive discounts of $20 \%$ and $10 \%$ are given on an item marked at $Rs. 700$. Find the selling price (in $Rs.$).

The selling price of an article is $Rs.\, 816$ if the discount on it is $15 \%$. What would be the selling price of the article $($ in $Rs.\,)$ if the discount on it is $25 \%$?

What was the rate of discount if a computer with a marked price of $Rs. 30,000$ was sold for $Rs. 28,000$? (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 $Rs.$)