(2) If it is difficult, first calculate the probability of three people working in different societies.
N (ω) = 125n (different clubs) =5*4*3=60 p (different clubs) =60/ 125= 12/25.
So the probability that at least two of the three people join the same club is1-12/25 =13/25.
(3)x conforms to the binomial distribution p(x=i)=(C above I below 3) * ((kloc-0//5) I) * ((4/5) (3-I)).
x 0 1 2 3
p 64/ 125 48/ 125 12/ 125 1/ 125
e(x)=(64/ 125)* 0+(48/ 125)* 1+( 12/ 125)* 2+( 1/ 125)* 3 = 3/5