A shopkeeper buys an article at $8$ for $Rs\,16$ and sells them at $9$ for $Rs\,20$. What is his gain or loss percent?

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 $Rs$ $4275 ?$

Find a simple discount equivalent to a discount series of $10 \%, 20 \%$ and $25 \%$ (in $\%$)

A shopkeeper sold Chairs at $Rs.\, 2139$ each after giving $7 \%$ discount on labelled price. Had he not given the discount, he would have earned a profit of $15 \%$ on the cost price. What was the cost price of each chairs? (in $Rs.$)

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 dairyman pays $Rs.\, 6.40$ per litre of milk. He adds water and sells the mixture at $Rs.\, 8$ per litre, thereby making $37.5\%$ profit. The proportion of water to milk received by the customers is