1. There must be exactly two possible outcomes (girl, boy).
2. Repeated trials must be independent.
3. The probabilities of the two outcomes don't change from trial to trial.
n = 3 (there are 3 children "generated")
p = 0.55 (the probability that a child is a girl)
The probability that a family of 3 consists of one girl and two boys is
[tex] _3C_1 \times (.55)^1 \times (.45)^2 = 3 \times .55 \times .2025 = 0.334125 [/tex]
In general, the probability that a binomially distributed random variable X is equal to r is
[tex] _nC_r \times p^r \times (1-p)^{n-r} [/tex]
