$A$ 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 $\%$)?

Abhishek purchased $140$ shirts and $250$ trousers at $Rs. 450$ and $Rs. 550$ respectively. What should be the overall average selling price of shirts and trousers so that $40 \%$ profit is earned? (in $Rs.$) (rounded off to the next integer)

By selling a book for $Rs. 360$,$20\%$ profit was earned. What is the $CP$ of the book in $Rs.$?

$A$ fruit vendor buys $10$ bananas for $Rs. 14$ and sells them at $12$ for $Rs. 15$. Find his percentage gain or loss.

$A$ man sells two articles for $Rs. 5000$ each,neither losing nor gaining in the deal. If he sold one of them at a gain of $25 \%$,the other article is sold at a loss of .......$\%$

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