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

$A$ man buys a single apple for $Rs. 25$. If he were to buy a dozen apples,he would have to pay a total amount of $Rs. 250$. What would be the approximate percent discount he would get on buying a dozen apples?

The price of a chair is $Rs.\, 500$. It has been sold at two successive discounts of $10\%$ each. What is its selling price? (in $Rs.$)

$A$ dealer marks a washing machine for $Rs.\, 7500$ and allows a discount of $6 \%$ on it. Find its selling price in $Rs.$

$A$ owes $B$ $Rs. 1350$ due in $3$ months and $B$ owes $A$ $Rs. 1078$ due in $5$ months. If they agree to settle their account right now at $5\%$ $p.a.$ simple interest,how much should $A$ pay to $B$ (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 $Rs.$)