The cost price of $100$ books is equal to the selling price of $60$ books. The gain or loss percentage will be:

On a $Rs. 10,000$ payment order,a person has a choice between three successive discounts of $10\%, 10\%$ and $30\%$ and three successive discounts of $40\%, 5\%$ and $5\%$. By choosing the better offer,how much can he save in $Rs.$?

$A$ tradesman gives $4 \%$ discount on the marked price and gives $1$ book free for buying every $15$ books and thus gains $35 \%$. The marked price is increased above the cost price by (approx.) (in $\%$).

$A$ trader sells rice at a profit of $5 \%$ and uses a weight which is $25 \%$ less. Find the total percentage gain.

$A$ shopkeeper sold chairs at $Rs. 2139$ each after giving a $7 \%$ discount on the labelled price. Had he not given the discount, he would have earned a profit of $15 \%$ on the cost price. What was the cost price of each chair? (in $Rs.$)

$A$ man purchased $120$ reams of paper at $Rs. 80$ per ream. He spent $Rs. 280$ on transportation,paid octroi at the rate of $40$ paise per ream,and paid $Rs. 72$ to a porter. In order to gain $8\%$ profit,he must sell each ream of paper for (in $Rs.$):