A man purchased $150$ pens at the rate of $Rs.\, 12$ per pen. He sold 50 pens at gain of $10 \% .$ The percentage gain at which he must sell the remaining pens so as to gain $15 \%$ on the whole outlay is……..$\%$

At a cost of $60$ paise per article, Sarika produces $750$ articles. She puts the selling price such that if only $600$ articles are sold, she would have made a profit of $40 \%$ on the outlay. However, $120$ articles got spoilt and she was able to sell $630$ articles at this price. Find her actual profit or loss percent as the percentage of total outlay assuming that the unsold articles are useless.

A person sells two articles, each for $Rs.\,1040.$ He incurs $20 \%$ loss on the first and $10 \%$ loss on the second. Find out overall percent loss.

A shopkeeper sells a badminton racket, whose marked price is $Rs.\, 30$, at a discount of $15 \%$ and gives a shuttle cock costing $Rs.$ $1.50$ free with each racket. Even then he makes a profit of $20\%.$ His cost price per racket is (in $Rs$)

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