The cost price of $100$ books is equal to the selling price of $60$ books. The gain percentage or loss percentage is:

The cost of an article including the sales tax is $Rs. 616$. The rate of sales tax is $10 \%$. If the shopkeeper has made a profit of $12 \%$,then the cost price of the article is in $Rs.$?

$A$ sells his house worth $Rs. 10\, lakh$ to $B$ at a loss of $10\%$. Later,$B$ sells it back to $A$ at $10\%$ profit. The result of the two transactions is:

An article is sold for $Rs. 4950$ at a gain of $10 \%$. What would have been the gain or loss per cent if it had been sold for $Rs. 4275$?

By selling an article for $Rs. 102$,there is a loss of $15 \%$. When the article is sold for $Rs. 134.40$,the net result in the transaction is:

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.