# Binomial conditional probability.

• Nov 12th 2011, 08:31 PM
mtingt
Binomial conditional probability.
A fair coin is tossed 5 times. What is the probability of obtaining exactly 2 heads if it is known that at least 1 head appeared?
• Nov 12th 2011, 08:41 PM
TKHunny
What is the probability of exactly one (1) "heads" in four tosses? Are you sure it's trickier than that? If so, why?
• Nov 12th 2011, 08:44 PM
mtingt
what do you mean?
• Nov 13th 2011, 10:49 AM
mr fantastic
Re: Binomial conditional probability.
Quote:

Originally Posted by mtingt
A fair coin is tossed 5 times. What is the probability of obtaining exactly 2 heads if it is known that at least 1 head appeared?

Let X be the random variable 'Number of heads'.

Calculate $Pr(X = 2 | X \geq 1)$ using the usual formula for conditional probability.