If the selling price is doubled,the profit triples. Find the profit percent.

$A$ sells an article to $B$ at a gain of $20 \%$,$B$ sells it to $C$ at a gain of $10 \%$,and $C$ sells it to $D$ at a gain of $12 \frac{1}{2} \%$. If $D$ pays $₹ 29.70$,then $A$ purchased the article for (in $₹$):

$A$ vendor bought toffees at $6$ for a rupee. How many for a rupee must he sell to gain $20 \%$?

$A$ shopkeeper bought $30\, Kg$ of wheat at the rate of $Rs.\, 45$ per $Kg$. He sold $40\%$ of the total quantity at the rate of $Rs.\, 50$ per $Kg$. Approximately,at what price per $Kg$ should he sell the remaining quantity to make $25\%$ overall profit? (in $Rs.$)

If the cost price of $21$ watches is equal to the selling price of $18$ watches,then what would be the gain percent in this transaction?

The ratio of cost price and selling price of an article is $25:26$. The percent of profit will be