Monty Hall problem: A apparently counter-intuitive problem in the probability which gets its name from the TV game show, 'Let's Make a Deal' hosted by the Monty Hall. On show a participant is shown three doors behind one of which is the valuable prize and behind the other two are the booby prizes. The participant selects the door and then, before the opted door is opened, the host opens one the two left behind doors to reveal one of the booby prizes. The participant is asked if he/she would like to stay with originally selected door or switch to the other, as yet, unopened door. Number of people think that the switching doors makes no difference to the probability of winning the valuable prize but several people are wrong because switching doubles this probability from a third to two thirds.