Answer :
Using the given formula, we have been able to prove that; the expected value of the students' score is 18 correct responses
How to solve binomial probability distribution problems?
1) Let X denote the number of correct guesses, assuming that a student guesses randomly among the five options of all 25 questions. Then X has a binomial probability distribution with;
n = 25
p = 1/5 = 0.2
2) Let Y denote the number of correct responses on the seven questions for which the student guesses randomly from among the five options. Then Y has a binomial probability distribution with n = 7 and p = 0.20. Then the expected value of Y is;
E(Y) = np = 7(0.2) = 1.4
Using the scoring formula given, we have;
Score = (18 + Y) - 0.25(7 - Y) + 0(0)
= 16.25 + 12Y
The expected value of the students' score is;
E(16.25 + 12Y) = 16.25 + 12(1.4)
= 18 correct responses.
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