A fair coin is tossed 11 times. What is the probability of obtaining exactly 9 heads if it is known that at least 1 head appeared? Round your answer to four decimal places.
+33661 With 1 head given for certain, you need exactly 8 more heads and 2 tails.
The probability of a given sequence of 8 heads and 2 tails is (1/2)8*(1/2)2 = 1/1024.
There are nCr(10,8) = 45 ways of achieving such a sequence, so the overall probability is 45/1024 = 0.0439 to four decimal places.
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+33661 With 1 head given for certain, you need exactly 8 more heads and 2 tails.
The probability of a given sequence of 8 heads and 2 tails is (1/2)8*(1/2)2 = 1/1024.
There are nCr(10,8) = 45 ways of achieving such a sequence, so the overall probability is 45/1024 = 0.0439 to four decimal places.
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