Answer
See below.
Work Step by Step
The problem is that although he is guaranteed to win, the prize is not guaranteed because there may be more people winning and then the prize is shared, so he might lose money.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.