① The opposite event: the first two people didn't win the prize, that is, the probability was (17/20) * (1619) = 71.6%, so the calculated probability was1-7/kloc-.
(2) or as the first person to draw, the second person also draws; Or the first person draws, and the second person fails; The first person can't draw, and the second person draws the union of three events, so the probability is (3/20) * (2/19)+(3/20) * (17/19)+(17/).
If the lottery ticket is put back, the probability of winning at least one of the first two people can be regarded as
① The opposite event: the first two players didn't win, that is, the probability was (17/20) * (17/20) = 72.25%, so the probability was.
1-72.25%=27.75%
(2) or as the first person to draw, the second person also draws; Or the first person draws, and the second person fails; The first person won't win, and the second person won the union of three events, so the probability is (3/20) * (3/20)+(3/20) * (17/20)+(17/20) * (3/20) =