Question

15. What z-score value separates the highest 10% of the scores in a normal distribution from the lowest 90%? 

a. z=1.28 

d. z=0.25

c. z=-1.28 

d. z=-0.25 

16. On an exam with μ= 52, you have a score of X = 56, Which value for the standard deviation would give you the highest position in the class distribution? 

a. σ=2 

b. σ=4

c. σ=8

d. Cannot be determine 

17. For a population with μ=80 and ơ=10, what is the z-score corresponding to X-95?

a. +0.25 b. +0.50 c. +0.75 d. +1.50 

18. What proportion of a normal distribution is located between the mean and z = 1.40? 

a. 0.9192 b. 0.0808 c. 0.4192 d. 0.8384 

19. A normal distribution has a mean of μ=70 with σ=12. If one score is randomly selected from this distribution, what is the probability that the score will be greater than X = 58? 

a. 0.8413 b. 0.1577 19, c. 0.3413 d. 0.6826 

20. John drives to work each morning, and the trip takes an average of μ=38 minutes. The distribution of driving times is approximately normal with a standard deviation of ơ=5 minutes. For a randomly selected morning, what is the probability that John's drive to work will take between 36 and 40 minutes? 

a. 0.079.3 b. 0.1526 c. 0.1554 d. 0.3108

Answer 1

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15. The Z-score which differentiates highest 10% from lower 90% has to have a score "c" such that:

P(X

We look up the Z tables to get the following as Z score:

so, c = 1.282

Hence, answer is a. Z = 1.28