$A$ trader buys $500 \, kg$ of cotton for $Rs. 9,000$. $10 \%$ of this cotton is spoiled due to rain. At what rate $(Rs./ kg)$ should he sell the rest to earn $10 \%$ profit?

Three successive discounts of $10 \%$,$12 \%$,and $15 \%$ are equivalent to a single discount of what percentage (in $\%$)?

Rahim bought a gift item for $Rs. 510$ after getting a discount of $15 \%$. He then sells it $5 \%$ above the marked price. The profit earned in this deal is (in $Rs.$)

The cost price of $12$ tables is equal to the selling price of $16$ tables. The loss percent is (in $\%$)

$A$ shopkeeper sold sarees at $Rs. 266$ each after giving a $5\%$ discount on the labelled price. Had he not given the discount,he would have earned a profit of $12\%$ on the cost price. What was the cost price of each saree? (in $Rs.$)

Ravi purchases $90$ pens and sells $40$ pens at a gain of $10 \%$ and $50$ pens at a gain of $20 \%$. Had he sold all of them at a uniform profit of $15 \%$,he would have got $Rs. 40$ less. Find the cost price of each pen in $Rs$.