$A$ man bought nine pens for a rupee. How many pens should he sell for a rupee to gain $50 \%$?

An electric pump was sold at a profit of $15 \%$. Had it been sold for $Rs. 600$, the profit would have been $20 \%$. What was the former selling price in $Rs.$?

$A$ shopkeeper mixes $20 \, kg$ of rice which cost him $Rs. \, 5$ per $kg$ with $35 \, kg$ of rice which cost him $Rs. \, 7$ per $kg$. Then he sells the mixture at $Rs. \, 6.5$ per $kg$. Find his total profit and percent profit.

$A$ man bought $4$ dozen eggs at $Rs. 24$ per dozen and $2$ dozen eggs at $Rs. 32$ per dozen. To gain $20\%$ on the whole,he should sell the eggs at what price in $Rs.$ per dozen?

$A$ man gains $20 \%$ by selling an article for a certain price. If he sells it at double the price,what will be the percentage of profit (in $\%$)?

$A$ reduction of $21\%$ in the price of an item enables a person to buy $3\, Kg$ more for $₹ 100$. The reduced price of the item per $Kg$ is (in $₹$):