An article which is marked at $Rs. 975$ is sold for $Rs. 897$. The percentage discount is?

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 $Rs.$?

$A$ shopkeeper sells $20$ pencils for the same amount of money as he paid for $25$ pencils. What is his gain percent?

$A$ cloth dealer professes to sell cotton at cost price, but uses a meter scale having a length of $80 \, cm$ only and charges for a full meter. Find his gain percent.

Find a simple discount equivalent to a discount series of $10 \%, 20 \%$ and $25 \%$ (in $\%$).

Nitin bought some oranges at $Rs. 40$ a dozen and an equal number at $Rs. 30$ a dozen. He sold them at $Rs. 45$ a dozen and made a profit of $Rs. 480$. The total number of dozens of oranges he bought was: