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# For one toss of a certain coin the probability that the

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05 Sep 2007, 00:29
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For one toss of a certain coin the probability that the outcome is heads is .6. If this coin is tossed 5 times, which of the following is the probability that the outcome will be heads at least 4 times.

A) (.6)^5
B) 2(.6)^4
C) 3((.6)^4)(.4)
D) 4((.6)^4)(.4) + (.6)^5
E) 5((.6)^4)(.4) + (.6)^5
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05 Sep 2007, 00:56

So we want either HHHHT or HHHHH.

HHHHT -> number of ways to arrange this word = 5!/4! = 5
Each way has a probability of (0.6)^4(0.4). 5 ways = 2(0.6)^4

HHHHH -> has a probability of (0.6)^5

Total = (0.6)^4(0.4)(5) + (0.6)^5.

Ans E
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