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

$A$ shopkeeper loses $7 \%$ by selling a cricket ball for $Rs. 31$. For how much should he sell the ball so as to gain $5 \%$? (in $Rs.$)

The cost price of an article is $64 \%$ of the marked price. Calculate the gain percent after allowing a discount of $12 \%$.

If a vendor sells a coconut at $Rs. 14.4$,he makes a $10 \%$ loss. If he wants to make a $25 \%$ profit,at what price (in $Rs.$) should he sell it?

$A$ shopkeeper sold an article offering a discount of $24 \%$ and earned a profit of $23.5 \%$. What would have been the percentage of profit earned if no discount had been offered?

Articles are marked at a price which gives a profit of $25 \%$. After allowing a certain discount,the profit reduces to $12\frac{1}{2} \%$. The discount percent is: (in $\%$)