a quiz has 20 multiple choice questions. each question has four possible choices. if a student makes a random guess on each question, what is the expected number of correct answers?

If a quiz has 20 multiple choice questions, then the expected number of correct answers is 5.

For each question, there are 4 possible choices, and only 1 of them is correct.

So, the probability of randomly guessing the "correct-answer" for any  question is = 1/4 = 0.25,

Each question is an independent event, we use the concept of linearity of expectation to calculate the expected number of correct answers for all 20 questions.

The "Expected" number of correct answers for a "single-question" is  probability of guessing it correctly, which is 0.25,

The "Expected-Number" of correct answers for 20 questions is the sum of the expected number of correct answers for each question,

⇒ Expected number of correct answers = (Probability of guessing a single question correctly) × (Number of questions),

Substituting the values,

We get,

⇒ Expected number of correct answers = 0.25 × 20,

⇒ Expected number of correct answers = 5

Therefore, the expected number of correct answers when making "random-guesses" on all 20 multiple choice questions is 5.

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