Question 4 (5 marks) The probability distribution table shows the probabilities of having 0, 1, 2 or 3 girls in a family
with 3 children.
1 2 3
3a3aa
P(X - x)
a Find the value for a.
[2]
121
b Find the expected value for the number of girls in a family with 3 children.
In a sample of 400 children, find the expected number of families that have 2 girls.