$A$ man buys an article for $Rs. 27.50$ and sells it for $Rs. 28.60$. Find the gain percent. (in $\%$)

$A$ reduction of $10 \%$ in the price of rice enables a person to obtain $25 \text{ kg}$ more for $Rs. 2250$. Find the reduced price per $\text{kg}$ of the rice (in $Rs.$).

$A$ manufacturer sells an article to a wholesale dealer at a profit of $20 \%$. The wholesale dealer sells it to a retail merchant at a loss of $5 \%$. Find out the resultant profit or loss.

If the ratio of the cost price and selling price of an article is $20: 21$,then what will be the profit percent (in $\%$)?

Ravi purchases $90$ pens and sells $40$ pens at a gain of $10 \%$ and $50$ pens at a gain of $20 \%$. Had he sold all of them at a uniform profit of $15 \%$,he would have got $Rs. 40$ less. Find the cost price of each pen in $Rs$.

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