# 2a. Find the Probability

• Feb 7th 2008, 01:41 AM
cu4mail
2a. Find the Probability
Plz help on this..

A class has 12 boys and 4 girls. Suppose three students are selected at random from the class. Find the probability P that they are all boys using Multiplication theorem for conditional probability.

• Feb 7th 2008, 02:13 AM
DivideBy0
Quote:

Originally Posted by cu4mail
Plz help on this..

A class has 12 boys and 4 girls. Suppose three students are selected at random from the class. Find the probability P that they are all boys using Multiplication theorem for conditional probability.

There are ${12 \choose 3}$ ways of picking 3 boys.
AND there are ${4 \choose 0}$ ways of picking 0 girls.
There are ${16 \choose 3}$ ways of picking three students.
So the probability is $\frac{{12 \choose 3} {4 \choose 0}}{{16 \choose 3}}=\frac{11}{28}$