Question

On an exam, the highest 10% of the scores earn a grade of A. If, of...

On an exam, the highest 10% of the scores earn a grade of A. If, of the 40 students who took the exam, 10 are selected at random:

a) what is the probability that exactly 2 of them received an A?

b) what is the probability that more than 2 of them received an A?

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Answer #1

Solution

Given that ,

Using binomial probability formula ,

P(X = x) = (n C x) * px * (1 - p)n - x

(a)

P(X = 2) = (10 C 2) * 0.102 * (0.90)8

Probability = 0.1937

(b)

P(x > 2) = 1 - P(x 2)

= 1 - 0.9298

= 0.0702

Probability = 0.0702

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