You have a $20 bill, and you need to double it. You have 1 month, you must keep it in cash (No banks, cashapp, credit cards), you don’t have an address, a phone number, or and you can’t interact to people in public. using just the internet and an email, how do you double the money?
No time constraint. So it’s very easy: you just follow a random person until they accidentally drop a $20 bill.