Question 635064
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Hi,
a. How many ways can 6 passengers be lined up to get on a train? {{{6! = 720}}} ways
b. If {{{highlight(a)}}} certain persons insist on following each other, how many ways are possible?
1) think of the {{{highlight(a)}}} persons as one unit (they themselves can be arranged a! ways)
2) then the units to arrange typically would be (6-a)
 {{{a!(6-a)!}}} ways this can be done