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

$A$ man buys $300$ dozen of bananas for $Rs. 3,600$. He sold $1/3$ of the stock at a loss of $10\%$ and the remaining $2/3$ of the stock at a gain of $10\%$. Find his overall percent profit or loss.

Sasha goes to a shop to buy a sofa set and a center table. She bargains for a $10 \%$ discount on the center table and a $25 \%$ discount on the sofa set. However,the manager,by mistake,interchanged the discount percentage figures while making the bill and Sasha paid accordingly. When compared to what she should have paid for her purchases,what percentage did Sasha pay extra,given that the center table costs $40 \%$ as much as the sofa set (in $\%$)?

If the cost price of $12$ pens is equal to the selling price of $8$ pens,find the gain percent.

Ajit calculates his profit percentage on the selling price,whereas Rohit calculates his on the cost price. They find that the difference between their profits is $Rs. 100$. If the selling price for both of them is the same and both of them get a $25\%$ profit,find their selling price (in $Rs.$).

If a stall sells a pizza at $Rs. 200$,he makes a $20 \%$ loss. If he wants to make a $10 \%$ profit,then at what price (in $Rs.$) should he sell it?