A shopkeeper purchased $70$ $kg$ of potatoes for $Rs.\, 420$ and sold the whole lot at the rate of $Rs.\, 6.5$ per $kg.$ What will be his gain percent?

A dishonest dealer use a scale of $90\, cm$ instead of a metre scale and claims to sell at cost price. His profit is in $\%$

Oil equal to $20 \%$ of the weight of ground nut is extracted in a mill. The matter left after extraction is sold as cattle feed at the rate of $Rs.\, 12.5$ per $kg$. The ground nuts are bought at $Rs.$ $20$ per $kg.$ the processing cost is $Rs.\, 5$ per $kg$. At what price $(Rs.$ per $kg$ ) should the oil be sold to earn $20 \%$ profit on total costs (Total cost $=$ cost of groundnuts and processing costs)?

By selling an article for $Rs$ $384,$ a trader gains $20 \%$. Find the cost price of article.

The market price of an article is $Rs.$ $100 .$ If the article is sold at a discount of $10 \%,$ then $35 \%$ profit is realised. How much loss or profit will be made if it is sold for $Rs.\, 30$ less than market price?

A shopkeeper sold two bicycles for $Rs.\,1500$ each. On one, he gains $25 \%$ and on the other he loses $20 \%$. His gain or loss per cent in the whole transaction is