If the selling price of $50$ articles is equal to the cost price of $40$ articles,then the loss or gain percent is:

$A$ trader buys goods at a $20 \%$ discount on the marked price. If he wants to make a profit of $25 \%$ after allowing a discount of $20 \%$ on his new marked price,by what percent should his new marked price be greater than the original marked price?

Nisha bought a number of oranges at $2$ for a rupee and an equal number at $3$ for a rupee. To make a profit of $20 \%$ she should sell a dozen for (in $Rs.$)

An article is marked for sale at $Rs. 504$. The shopkeeper gives a discount of $5\%$ on the marked price and still earns a profit of $20\%$. What is the cost price of the article? (in $Rs.$)

$A$ fruit seller sells mangoes at the rate of $Rs. 9$ per $kg$ and thereby loses $20\%$. At what price per $kg$ should he have sold them to make a profit of $5\%$? (in $Rs.$)

The labelled price of a cupboard is $Rs. 6500$. The shopkeeper sold it by giving $5\%$ discount on the labelled price and earned a profit of $15\%$. What approximately is the cost price of the cupboard? (in $Rs.$)