Ravipurchases $90$ pens and sells $40$ pens at a gain of $10 \%$ and $50$ pens at a gain of $20 \% .$ Had he sold all of them at a uniform profit of $15 \%$ he would have got $Rs.\, 40$ less. Find the cost price of each pen in $Rs.$

An item costing $Rs.\, 200$ is being sold at $10 \%$ loss. If the price is further reduced by $5 \%,$ the selling price will be (in $Rs.$)

A trader mixes $26\, kg$ of rice at $Rs$. $20$ per $kg$ with $30\, kg$ of rice of other variety at $Rs.\, 36$ per $kg$ and sells the mixture at $Rs.\, 30$ per $kg.$ His profit percent is

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)?

A man bought $15$ mangoes for a rupee. How many mangoes were sold for a rupee so that there is a loss of $25 \% ?$

By selling an umbrella for $Rs.\, 300,$ a shopkeeper gains $20 \%$. During a clearance sale, the shopkeeper allows a discount of $10 \%$ on the marked price. His gain per cent during the sale is