Riddle: A man has one phone, and wants to dail 5 different numbers to call 5 different people.
The man can only use the phone 10 times. And the man does not know the numbers of the five people he wants to call.
He only knows one number, and that number isn't the number of any of the 5 people he wants to call. In the end he ends up calling all of the people and he ended up dailing the same number he knew from the beginning 5 times. What is the number that he knew from the begginning?
Answer: The number that the man knew was 411, he dailed 411 five times to get the numbers of the five people and ended up using the phone 10 times.