Question 1172380: Two coins are tossed. what is the probability that the one coins shows heads if it is known that at least one coin is tails?
Answer by math_tutor2020(3817)   (Show Source):
You can put this solution on YOUR website!
"at least one coin is tails" is another way of saying "one or more coins is tails"
Here are all the possible outcomes of flipping 2 coins
HH
HT
TH
TT
where H = heads and T = tails
The outcomes
HT
TH
TT
all represent cases when we get at least one tail. All we've effectively done is kick out HH
There are 2 cases when we get heads (HT and TH) out of three cases mentioned above.
The probability of showing heads, given this reduced sample space, is 2/3.
If we know there's at least one tail, then the probability of getting heads is 2/3.
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Answer: 2/3
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