Math question (Probability)?

[匿名]

2015-11-29 10:03 am

1. Three classes 4A, 4B and 4C attend a quiz contest. 3 representatives from each class will answer 10 questions. If any representative answers a question correctly, the class will get 10 marks; otherwise the class will get no marks. The probabilities that each of the representatives of 4C can answer a question correctly are 0.6, 0.8 and 0.75 respectively.

P(4C will get 10 marks after answering a question) = 0.98

If 4A and 4B got 80 and 60 marls respectively after answering the questions, find the probability that only 4C will win the contest, cor. to 4 decimal places.

2. If Kenny passes a mock exam, the probability that he passes the public exam is 0.8.If he fails the mock exam, the probability that he fails the public exam is 0.6. If the probability that Kenny passes the mock exam is 0.7, the probability that she passes the public exam is?

Please answer answer as many as you can.thx

回答 (1)

用戶46949

2015-11-30 8:13 am

✔ 最佳答案

1.　P(all 3 representatives in 4C can't answer correctly)=0.4*0.2*0.25=0.02
P(4C will get 10 marks after answering a question)=1-0.02=0.98

4A & 4B got 80 and 60 . If 4C will, they have to get 90 or 100 marks
P(4C got 90 marks or 100marks)
=10C9 (0.98^9 )*(0.02^1)+(0.98)^10=0.9838

2 P(passes the public exam)
=P(passes the mock exam & passes the public exam)+P(fail the mock exam & passes the public exam)
=0.7*0.8+0.3*(1-0.6)
=0.56+0.12
=0.68

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