Six students took part in the speech contest. They first draw lots to decide that the order of appearance is 1, 2, 3, 4, 5, 6, and the problem is 1.

This topic is unreasonable ... where were A and B drawn? .. If A draws first, the probability of not drawing on the 6th is 5/6. If you draw for the second time, there are two probabilities. The first one is that the first one is painted on the sixth symbol, the second one is that the first one is not painted on the sixth symbol ... and so on ~ ~ plus B's ... you must find one.