    Question

# On a multiple choice examination there are three possible answers for each of the five questions, then the probability that a candidate would get four or more correct answers just by guessing is:

A
11243
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B
1243
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C
1181
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D
181
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Solution

## The correct option is A 11243In this question, we have the repeated correct answer guessing form the given multiple choice question are Bernoulli trials Let us now assume, X represents the number of correct answer by guessing in the multiple choice set. Now, probability of getting a correct answer, p=1/3 Thus, q=1−p=1−1/3=2/3 Clearly, we have X is a binomial distribution where n=5 and p=1/3 ∴P(X=x)=nCxqn−xpx =5Cx(23)5−x×(13)x Hence, probability of guessing more than 4 correct answer = P(X≥4)=P(x=4)+P(x=5)=5C4(23)×(13)4+5C5(13)5=5×23×181+1×1243=11243  Suggest Corrections  3      Similar questions
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