Aditya purchased a book with a $20 \%$ discount on the marked price. How much $Rs.$ did he pay if the marked price of the book was $Rs. 500$?

Some articles were bought at $6$ for $Rs. 5$ and sold at $5$ for $Rs. 6$. The gain percent is:

$A$ shopkeeper gains the cost of $8$ metres of thread by selling $40$ metres of thread. Find his gain percent.

The profit earned by selling an article for $Rs. 832$ is equal to the loss incurred when the same article is sold for $Rs. 448$. What should be the selling price for making $50\%$ profit? (in $Rs.$)

$A$ man buys $10$ oranges for a rupee and sells $8$ oranges for a rupee. What is the profit percent?

Aditya bought a scooter for a certain sum of money. He spent $15 \%$ of the cost price on repairs and sold it for a profit of $Rs. 1104$. What did he spend on repairs if the profit he earned was $20 \%$?