Question

有10道ABCD单选题,答对6道以上算及格,问瞎选蒙及格的概率是多少?

Answer 1

P(及格)

=P(6道题目对)+P(7道题目对)+P(8道题目对)+P(9道题目对)+P(10道题目对)

=(10C6)(3/4)^4.(1/4)^6+(10C7)(3/4)^3.(1/4)^7+(10C8)(3/4)^2.(1/4)^8+(10C9)(3/4).(1/4)^9

+(10C10)(1/4)^10

=0.0197