A lot of people risk money with bets on sport events or other events. Bookkeepers that offer such bets earn a lot of money. We are making a proposal (more exactly: a concept for a part of a basic mathematics course) for learning mathematics behind the screen (internet bets are very popular). Learners should organize a "sports event" (more precisely: some kind of simulation of such an event), find several different types of bet offices and offer odds. Other participants (learners) get game money and bet. When the event is over and the results are fixed the learners calculate wins and losses. So they learn how to calculate odds and why bookkeepers earn so much money--if the bookkeepers know enough about mathematics and other things they need to know. By considering discovery-teaching-methods students should recognize the mathematical facts while thinking about bets and odds. Reflecting the results learners learn something important about the real world: It is better to avoid bets!