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you have taken the probability of 7 tails and 1 head as 1/(2^8). This is correct for any 1 particular position of head. But here the 1 head can occur in any of the 8 positions. So you should have taken 8* 1/(2^8).
plus all tails has the probability of 1/(2^8)
so probability of 7T,1H or 8T,0H is (8+1)/(2^8) = 9/256
Re: A gmat prep. is this correct?
20 Jul 2008, 07:54