By selling $80$ ball pens for $₹ 140$,a retailer loses $30 \%$. How many ball pens should he sell for $₹ 104$ so as to make a profit of $30 \%$?

By selling an article for $Rs. 21$,a man incurs a loss such that the percentage loss is equal to the cost price. The cost price of the article is (in $Rs.$):

$A$ man bought $4$ dozen eggs at $Rs. 24$ per dozen and $2$ dozen eggs at $Rs. 32$ per dozen. To gain $20\%$ on the whole,he should sell the eggs at what price in $Rs.$ per dozen?

$A$ sells an article to $B$ for $₹ 45,000$ losing $10 \%$ in the transaction. $B$ sells it to $C$ at a price which would have given a profit of $10 \%$ to $A$. By what per cent does $B$ gain?

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

Successive discounts of $10 \%$,$12 \%$ and $15 \%$ are equivalent to a single discount of: