A committee of 5 people is to be selected from student council. Council has 6 boys and 7 girls. What is the probability that the committee will have at least 3 boys?
The other tutor's solution is wrong.
We get the probability of the complement event
and subtract from 1. The complement event is a committee with
no boys or 1 boy or 2 boys.
1 - P(0 boys OR 1 boy OR 2 boys)
"OR" means "ADD"
1 - [P(0 boys)+P(1 boy)+P(2 boys)]
P(0 boys) = P(5 girls) =
P(1 boy) = P(4 girls AND 1 boy)
"AND" means "MULTIPLY", so
P(1 boy) = P(4 girls AND 1 boy) =
P(2 boys) = P(3 girls AND 2 boys) =
So,
1 - [P(0 boys)+P(1 boy)+P(2 boys)]
becomes:
1 - []=
Edwin