Answer :

We have been given that, there are 3 possible answers of the total 5 questions out of which only 1 answer is correct.


Let p be the probability of getting a correct answer out of the 3 alternative answers.



Then, q is the probability of not getting a correct answer out of 3 alternatives.


And, p + q = 1


q = 1 – p





Let X be any random variable representing a number of correct answers just be guessing out of 5 questions.


Then, the probability that the candidate would get r answers correct by just guessing out of 5 questions is given by this Binomial distribution.


P (X = r) = nCrprqn-r


Here, n = 5.


Substitute the value of n, p, and q in the above formula.


…(i)


We need to find the probability that a candidate would get four or more correct answers just by guessing.


The probability can be expressed as,


Probability = P (X ≥ 4)


This is in turn can be written as,


P (X ≥ 4) = P (X = 4) + P (X = 5)


Put r = 4, 5 subsequently in equation (i) and then substitute in the above formula.









P (X ≥ 4) = 0.0453


Hence, the probability that a candidate would get four or more correct answers just by guessing is 0.0453.


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