If the $CP$ of $50$ items is equal to the $SP$ of $40$ items,then what is the profit or loss $\%$ (in $\%$)?

Seema sells a pen to Sapna at a profit of $25 \%$. Sapna sells it to Asha at a profit of $10 \%$ and Asha sells it to Kavita at a profit of $5 \%$. If Asha sells it for $Rs.\,231$,find the cost price at which Seema bought the pen? (in $Rs.$)

Raheem sells a machine for $RS. 48$ lakh at a loss. Had he sold it for $RS. 60$ lakh,his gain would have been $5$ times the former loss. Find the cost price of the machine in lakh $Rs.$?

$A$ shopkeeper sells goods at $10 \%$ loss on cost price,but uses $20 \%$ less weight. What is his profit or loss percentage?

Arun purchased $30 \, kg$ of wheat at the rate of $Rs. \, 11.50$ per $kg$ and $20 \, kg$ of wheat at the rate of $Rs. \, 14.25$ per $kg$. He mixed the two and sold the mixture. Approximately at what price per $kg$ should he sell the mixture to make $30 \%$ profit? (in $Rs.$)

Anil bought an item with $12 \frac{1}{2} \%$ discount on the labelled price. He sold the item with $17 \frac{1}{2} \%$ profit on the labelled price. What was his percent profit on the price he bought?