主题：【原创】问道概率题 -- baiqi

Yes, you are right.

Event B is actually a series of events. In the expression 5 / (100 - 20), the number "20" should be replaced in each different row.

For example, in the second row, the tallest one amount the first 20 persons is the 21'st guy in height. Therefore, (100 - 21) persons MAY be picked, but only 5 of them are desired. The probability of event B in this case/row is 5 / (100 - 21).