# Math Contest Problem 3

• March 12th 2011, 08:05 PM
eric1299171
Math Contest Problem 3
This problem is from the 2002 Luzerne County Math Contest:
Assume a person flips five fair coins. What is the probability of obtaining at least 4 heads?
Is there any way to do this problem without listing all the possibilites? Thanks in advance!
• March 12th 2011, 08:49 PM
CaptainBlack
Quote:

Originally Posted by eric1299171
This problem is from the 2002 Luzerne County Math Contest:
Assume a person flips five fair coins. What is the probability of obtaining at least 4 heads?
Is there any way to do this problem without listing all the possibilites? Thanks in advance!

The number of heads in five flips is a binomial random variable $X \sim B(5,0.5)$, and you are asked to find:

$p=Pr(X=5)+Pr(X=4)$

CB
• March 20th 2011, 01:43 PM
eric1299171
Thanks for the reply! I looked up the formula in a probability book I had. =)