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?
2019-05-27
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?
优质解答
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
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