$A$ 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?

Seema sells a pen to Sapna at a profit of $25 \%$. Sapna sells it to Asha at a profit of $10 \%$ and Asha sells it to Kavita at a profit of $5 \%$. If Asha sells it for $Rs.\,231$,find the cost price at which Seema bought the pen? (in $Rs.$)

$A$ shopkeeper sells $25$ articles at $Rs. 45$ per article after giving a $10 \%$ discount and earns a $50 \%$ profit. If no discount is given,the profit percentage gained is......$\%$

Amit purchased $13$ chairs for $Rs. 115$ each and sold all of them for $Rs. 1220$. Find the profit or loss on the transaction.

$A$ cab driver makes a profit of $20 \%$ on every trip when he carries $3$ passengers and the price of petrol is $Rs. 30$ a litre. Find the percentage profit for the same journey if he goes with four passengers per trip and the price of petrol reduces to $Rs. 24$ a litre? (in $\%$)
(Assume that revenue per passenger is the same in both the cases.)

Find $SP$ when $CP = Rs. 80.40$ and $\text{loss} = 5\%$.