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?

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 $\%$)

$A$ shopkeeper allows a discount of $10 \%$ on the marked price of a camera. The marked price of the camera,which costs him $₹ 600$,to make a profit of $20 \%$ should be (in $₹$):

If a shopkeeper wants to give a $20 \%$ discount on a toy, he has to sell it for $Rs. 300$. If he sells it at $Rs. 405$, then his gain percent is: (in $\%$)

$A$ shopkeeper sells notebooks at the rate of $Rs.\, 45$ each and earns a commission of $4 \%$. He also sells pencil boxes at the rate of $Rs.\, 80$ each and earns a commission of $20 \%$. How much total commission will he earn in two weeks if he sells $10$ notebooks and $6$ pencil boxes a day? (in $Rs.$)

Surbhi bought a combined total of $25$ i-pads and i-phones. She marked up the i-pad by $20 \%$ on the cost price,while each i-phone was marked up by $Rs. 2000$. She was able to sell $75 \%$ of the i-pads and $2$ i-phones and make a profit of $Rs. 49000$. The remaining i-pads and $3$ i-phones could not be sold by her. Find her overall profit or loss if she gets no return on unsold items and it is known that an i-phone costs $50 \%$ of an i-pad.