$A$ trader marked the selling price of an article at $10 \%$ above the cost price. At the time of selling,he allows a certain discount and suffers a loss of $1 \%$. He allowed a discount of $\%$:

Vijay sold a watch at a gain of $5 \%$. Had he sold it for $Rs. 72$ more,he would have gained $13 \%$. Find out the cost price of the watch (in $Rs.$).

$A$ dealer sold a bicycle at a profit of $10 \%$. Had he bought the bicycle at $10 \%$ less price and sold it at a price $Rs. 60$ more,he would have gained $25 \%$. The cost price of the bicycle was:

If the cost price of $12$ pens is equal to the selling price of $8$ pens,find the gain percent.

Ravi purchases $90$ 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 $Rs$.

The profit earned by selling an article for $Rs. 832$ is equal to the loss incurred when the same article is sold for $Rs. 448$. What should be the selling price for making $50\%$ profit? (in $Rs.$)