If the cost price of $20$ articles is equal to the selling price of $15$ articles,find the profit percent?

Charging $30 \%$ above its production cost,a radio maker puts a label of $Rs. 286$ on a radio as its price. But at the time of selling it,he allows a $10 \%$ discount on the labeled price. What will his gain be? (in $Rs.$)

$A$ shopkeeper mixes $26 \, kg$ of wheat which costs $Rs. 20$ per $kg$ with $30 \, kg$ of wheat which costs $Rs. 36$ per $kg$ and sells the mixture at $Rs. 30$ per $kg$. Find the profit percent. (in $\%$)

The percentage profit earned by selling an article for $Rs. 1920$ is equal to the percentage loss incurred by selling the same article for $Rs. 1280$. At what price should the article be sold to make $25 \%$ profit? (in $Rs.$)

When Ram sold his book for $Rs. 255$,he made a loss of $15\%$. For how much should he have sold it if he wanted to make a profit of $5\%$?

If a discount of $10 \%$ is given on the marked price of a radio,the gain is $20 \%$. If the discount is increased to $20 \%$,the gain is......$\%$