An article is sold at a profit of $20 \%$. If both the cost price and selling price are $Rs. 150$ less,the profit would be $5 \%$ more. Find the cost price.

$A$ tradesman gives $4 \%$ discount on the marked price and gives $1$ book free for buying every $15$ books and thus gains $35 \%$. The marked price is increased above the cost price by (approx.) (in $\%$).

Raman sells a machine for $Rs. 39$ lakh at a loss. Had he sold it for $Rs. 49$ lakh,his gain would have been three times the loss. What is the cost price of the machine? (in $Rs. \text{ lakh}$)

Nutan pays $Rs. 2140$ for $3$ calculators and $4$ pens,while she pays $Rs. 1355$ for $1$ additional calculator and $5$ pens. What is the cost of a calculator in $Rs.$?

There would be a $10 \%$ loss,if rice is sold at $Rs. 54$ per $kg$. To earn a profit of $20 \%$,the price of rice per $kg$ will be (in $Rs.$)

On selling $17$ balls at $₹720,$ there is a loss equal to the cost price of $5$ balls. The cost price of a ball is