A person has $50 and spends $20. How much money do they have left?

To determine how much money the person has left after spending some, we start with the total amount they initially had, which is $50. After spending $20, we subtract that amount from the original total.

The calculation is as follows: $50 (initial amount) - $20 (amount spent) = $30 (remaining amount).

This logical step confirms that the person has $30 left after the expenditure. The answer reflects a straightforward arithmetic operation, showcasing an understanding of basic subtraction in a financial context.