The idiom 'Burn the midnight oil' means 'To work late into the night'. This idiom originates from the days before electric lighting, when people used oil lamps for light, especially when they stayed up late at night to read, write, or study. The phrase figuratively refers to working very late hours, often past midnight, to accomplish a task.
Understanding idioms involves recognizing that their meanings cannot typically be deduced from the literal meanings of their individual words. In the case of this idiom:
A shopkeeper buys an item for Rs 2000 and marks it up by 50% to set the marked price. He then offers a 20% discount on the marked price. What is the profit earned by the shopkeeper?