A professor knows from past experience that the time for students to complete a

Question

A professor knows from past experience that the time for students to complete a quiz is normally distributed with mean 21 minutes and standard deviation 4 minutes.

(a) If he allows 26 minutes for the quiz, what percent ( ± ± 0.1) of the students will not complete the quiz? (use Table A)

About __% of the students will not complete the quiz

(b) Suppose that he wants to allow sufficient time so that 95% of the students will complete the quiz in the allotted time.

How much time ( ± ± 0.1) should he allow for the quiz? About___ minutes

Explanation / Answer

Ans:

a)

z=(26-21)/4

z=1.25

P(z>1.25)=0.106 or 10.6% of the students will not complete the quiz

b)

P(Z<=z)=0.95

z=1.645

Sufficient time allowed=21+1.645*4=27.6 minutes

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