Assuming order doesn't matter:
From the total 4 people, you choose 2 - this is [tex]\binom42=6[/tex].
From the remaining 2 people, you choose 1 - this is [tex]\binom21=2[/tex].
From the last person, you choose that person - this is [tex]\binom11=1[/tex]
So there are 6*2*1 = 12 possible ways.
Note: [tex]\binom ab=\frac{a!}{b!(a-b)!}[/tex] is the binomial coefficient
