The simple interest and the true discount on a certain sum for a given time and at a given rate are $Rs.\, 85$ and $Rs.\, 80$ respectively. The sum is (in $Rs.$)

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

An article is marked $40 \%$ above the cost price and a discount of $30 \%$ is allowed. What is the gain or loss percentage?

The present worth of $Rs. 920$ due at the end of $3$ years at $5\%$ simple interest per annum is (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 $Rs.$)

$A$ bill which is due at the end of $4 \text{ years}$ is now worth $Rs. 575$,but if it is due in $2 \frac{1}{2} \text{ years}$,it would now be worth $Rs. 620$. The sum of the bill is (in $Rs.$)