Some articles were bought at $6$ articles for $Rs.\,5$ and sold at $5$ articles for $Rs.$ $6 .$ Gain percent is

A man purchases some oranges at the rate of $3$ for $Rs.\,40$ and the same quantity at $5$ for $Rs.\, 60.$ If he sells all the oranges at the rate of $3$ for $Rs.\, 50,$ find his gain or loss percent (to the nearest integer).

The $CP$ of $19$ article is equal to the selling price of $15$ article. Gain $\%$ is?

A person sells $36$ oranges per $Rs.\, 1$ and makes a loss of $4 \% .$ Find how many oranges per $Rs$ to be sold to have a gain of $8 \% ?$

A trader allows a trade discount of $20 \%$ and a cash discount of $6 \frac{1}{4} \%$ on the marked price of the goods and gets a net gain of $20 \%$ of the cost. By how much above the cost should the goods be marked for the sale? (in $\%$)

Ravipurchases $90$ 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 $Rs.$