Q.1 One day your teacher surprised you with a 21-questionmultiple-choice quiz. E

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Q.1 One day your teacher surprised you with a 21-questionmultiple-choice quiz. Each question has 5 possible answers, onlyone of which is correct.
If you answer the questions completely based on guessing, what isthe probability that: a) You will answer exactly 5 correctly?
b) You will answer at least 1 correctly?
c) You will answer at most 3 correctly? Q.1 One day your teacher surprised you with a 21-questionmultiple-choice quiz. Each question has 5 possible answers, onlyone of which is correct.
If you answer the questions completely based on guessing, what isthe probability that: a) You will answer exactly 5 correctly?
b) You will answer at least 1 correctly?
c) You will answer at most 3 correctly?

Explanation / Answer

This is a typical binomial probability question Let X be the number of correct answer X~Binomial (n = 21, p = 0.2) (a) P( X = 5) = 21C5 x (0.2)5 x(0.8)16 = 0.1833 (b) P(X >=1) = 1 - P(X = 0) = 1 - 21C0 x(0.2)0 x (0.8)21 = 1 - 0.0092 =0.9908 (c) P(X

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