Several psychology students are unprepared for a surprise true/false test with 1

Question

Several psychology students are unprepared for a surprise true/false test with 19 questions, and all of their answers arc guesses. Find the mean and standard deviation for the number of correct answers for such students, Would it be unusual for a student to-pass by guessing and getting at least 17 correct answers? Why or why not? Choose the correct answer below. Yes, because 17 is greater than the maximum usual value. Yes, because 17 is within the range of usual values. Yes, because 17 is below the minimum usual value. No, because 17 is within the range of usual values.

Explanation / Answer

a)

Here, n = 19, p = 0.5. Thus,

u = n p = 19*0.5 = 9.5 [ANSWER]

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b)

sigma = sqrt(np(1-p)) = sqrt(19*0.5*(1-0.5)) = 2.179449472 [ANSWER]

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c)

The maximum usual value is

u + 2*sigma = 9.5 + 2*2.179449472 = 13.85889894

Thus, as 17 exceeds this, then

OPTION A: Yes, becasue 17 is greater than the maximum usual value.

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