For one toss of a certain coin, the probability that the outcome is heads is 0.6. 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) (0.6)^5
(B) 2(0.6)^4
(C) 3(0.6)^4(0.4)
(D) 4(0.6)^4(0.4) + (0.6)^5
(E) 5(0.6)^4(0.4) + (0.6)^5
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【答案】E
【思路】最少有四次的頭表示 : 四次有頭的機率(不管順序) + 五次全頭的機率
請問四次有頭的機率為什麼要*5