$A$ person purchases $8$ pens for ₹ $10$ and sells $10$ pens for ₹ $8$. How much profit or loss percentage does he make?

$A$ shopkeeper buys articles at $8$ for $Rs\,16$ and sells them at $9$ for $Rs\,20$. What is his gain or loss percent?

By selling $25$ $metres$ of cloth,a trader gains the selling price of $5$ $metres$ of cloth. The gain of the trader in $\%$ is:

$A$ man sold two cows at $Rs. 1995$ each. On one he lost $10\%$ and on the other he gained $10\%$. What is his gain or loss percent (in $\%$)?

$A$ shopkeeper sells notebooks at the rate of $Rs. 457$ each and earns a commission of $4\%$. He also sells pencil boxes at the rate of $Rs. 80$ each and earns a commission of $20\%$. How much total commission will he earn in two weeks if he sells $10$ notebooks and $6$ pencil boxes a day?

$A$ man bought oranges at the rate of $8$ for $Rs. 34$ and sold them at the rate of $12$ for $Rs. 57$. How many oranges should be sold to earn a net profit of $Rs. 45$?