The idiom 'At the drop of a hat' means to do something immediately without any delay or hesitation. This phrase is often used to describe actions that are undertaken promptly and spontaneously. For instance, if someone is willing to help you at the drop of a hat, they are ready to assist you right away, without having to think about it.
When examining the given options:
Therefore, the correct answer is To do something immediately.
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?