There are 6 MC questions in a short quiz and 5 options are given for each question 2 marks are awarded for a correct answer and 1 mark is deducted for a wrong answer. If a student answers the questions by guessing find the probability that
A) His total score is negative
B) His total score is positive
Probability ..... plx help
2008-01-09 9:58 pm
回答 (2)
2008-01-10 8:28 am
✔ 最佳答案
If he answers 1 questions correctly, he can answer 2 more question wrongly that his score is 0.Therefore,
P(positive)
= P(answering at least 3 questions correctly)
= 6C3 x (1/5)(1/5)(1/5)(4/5)(4/5)(4/5) + 6C4 x (1/5)4 (4/5)2
+ 6C5 x (1/5)5 (4/5) + (1/5)6
= 309 / 3125
P (0 marks)
= P(answering exactly 2 questions correctly)
= 6C2 x (1/5)2 (4/5)4
= 768 / 3125
P(negative)
= 1 - P(positive) - P(0 marks)
= 2048 / 3125
2008-01-09 10:21 pm
A.
P(Negative Score) = P(1 Question is correct) + P(0 Question is correct)
P(1 correct) = (6 choose 1) (1/5)
P(0 correct) = 4/5*4/5*4/5*4/5*4/5*4/5
B.
P(Positive Score) = 1 - P(Neagative) - P(Getting a score of zero which is 2Question is correct)
P(2 correct) = (6 choose 2) (1/5)
=> The rest u do it urself baby.
P(Negative Score) = P(1 Question is correct) + P(0 Question is correct)
P(1 correct) = (6 choose 1) (1/5)
P(0 correct) = 4/5*4/5*4/5*4/5*4/5*4/5
B.
P(Positive Score) = 1 - P(Neagative) - P(Getting a score of zero which is 2Question is correct)
P(2 correct) = (6 choose 2) (1/5)
=> The rest u do it urself baby.
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