PREP-T2-PS-Q89

[GC06]

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

答案是E
請問要怎麼解比較快阿?

[Enriqueta]

please refer to
http://www.formosamba.com/phpBB3/viewtopic.php?t=26836