SOLUTION: you flip three coins. What is the probabilty that you get at least two heads, fiven that you get at least one head?

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Question 575605: you flip three coins. What is the probabilty that you get at least two heads, fiven that you get at least one head?
Answer by richard1234(7193) About Me  (Show Source):
You can put this solution on YOUR website!
This one can be tricky (read about the "Boy or Girl paradox" http://en.wikipedia.org/wiki/Boy_or_Girl_paradox) because it does not specify which coin is a head, just that at least one is a head. I would probably list all of the possibilities in our sample space:

HHH
HHT
HTH
THH
HTT
THT
TTH

(TTT cannot be in our sample space). Therefore there are seven possibilities, and four of them have at least two heads. The probability is 4/7.

This is similar to the Boy or Girl paradox, which states that a mother has two children; at least one of them is a boy. Surprisingly, the probability that both children are boys is 1/3, not 1/2. However, if you stated something comparative, such as "the older child is a boy" then the probability would be 1/2.