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 $Rs.$?

If the cost price of an item is $\frac{2}{5}$ of its marked price and if it is sold at a discount of $10 \%,$ then there will be

$A$ merchant advertises $10 \%$ off on the items bought from his store. The total discount obtained by a customer who bought a cooker worth $Rs. 650$,a heater worth $Rs. 500$,and a bag worth $Rs. 65$ is (in $Rs.$): (in $.50$)

$A$ sells a bicycle to $B$ at a profit of $20 \%$ and $B$ sells it to $C$ at a profit of $25 \%$. If $C$ pays $Rs. 1500$,what did $A$ pay for it in $Rs.$?

$A$ sold a horse to $B$ for $Rs. 4800$ by losing $20\%$. $B$ sells it to $C$ at a price which would have given $A$ a profit of $15\%$. $B$'s gain is (in $Rs.$)

The cost price of $40$ articles is the same as the selling price of $25$ articles. Find the gain percent. (in $\%$)