Stat Quiz #4

Click the answer button to see the answer.

  1. On the basis of chance, the probability of obtaining a value which falls between z = .50 and z = l.00 under the standard normal curve is approximately:
    a. 5 in a hundred
    b. 34 in a hundred
    c. l5 in a hundred
    d. 20 in a hundred

  2. For a normal distribution with a mean of 55 and a standard deviation of 4, what is the probability of selecting a score either greater than 56 or less then 5l?
    a. 0.7574
    b. 0.0637
    c. 0.2426
    d. 0.5600

  3. At z-score 2.5 the standard normal curve is the same height as at z-score:
    a. 0
    b. -2.5
    c. 5.2
    d. 5.2

  4. The test scores of 600 students are normally distributed with a mean of 76 and a standard deviation of 8. The instructor in the class had decreed that l0% of the students will fail the test. What score is at the upper limit of the range which defines failure?
    a. 86.24
    b. 76.32
    c. 65.76
    d. 72.82

  5. What proportion of cases in a normally distributed population will have z-scores greater than l.0 or less than -l.0?
    a. .l0
    b. 0.32
    c. 0.50
    d. 0.68

  6. A given distribution has a mean of 50. A score of 43 has a corresponding z-score of l.94. What is the standard deviation (to the nearest hundredth)?
    a. 3.6
    b. l2.96
    c. 3.6
    d. None of these.

  7. Given a normal distribution with a mean of 80 and a standard deviation of 5, we know that approximately what percent of the values are between 70 and 90?
    a. 68
    b. 95
    c. 99
    d. 99.7

  8. What is the probability that a value picked at random from the standard normal distribution will be between -1.96 and 1.96?
    a. 0.997
    b. 0.90
    c. 0.68
    d. 0.95

  9. Entrance examination scores made by students at a certain university are normally distributed with a mean of 600 and a standard deviation of 100. Approximately what proportion of the scores are greater than 900?
    a. 0.005
    b. 0.05
    c. 0.0013
    d. 0.10

  10. The test scores of 600 students are normally distributed with a mean of 76 and a standard deviation of 8. The number of students scoring 90 and above is:
    a. 175
    b. 24
    c. 276
    d. 576

  11. Which of the following statements is true?
    a. There are an infinite number of normal distributions.
    b. The area under a normal curve is approximately equal to 1.
    c. For the standard normal distribution, it is impossible to have a z value of 10.8.
    d. A normal distribution can always be used to accurately approximate a binomial probability value.

  12. The test scores of 600 students are normally distributed with a mean of 76 and a standard deviation of 8. The number of students scoring between 70 and 82 is:
    a. 328
    b. 164
    c. 260
    d. 272

  13. Suppose X is a random variable with mean = 190 and standard deviation = 10. For a sample of n = 25, which of the following statements is equivalent to P(mean(x) > 195)?
    a. P(z < 2.5)
    b. P(z > 2.5)
    c. P(z < 1)
    d. P(z > 1)

  14. For a t distribution, 90% of the area lies under the curve and between t = 1.89 and t = 1.89 if df = ?
    a. 2
    b. 3
    c. 7
    d. 8

  15. T scores are normal scores with a mean of 50 and a standard deviation of 10. What percent of the T scores would be expected to fall between T scores of 40 and 60?
    a. 20
    b. 34
    c. 50
    d. 68

  16. As the standard deviation of a normal distribution increases, the height of the normal curve increases.
    a. True
    b. False

  17. Normal distributions are discrete distributions.
    a. True
    b. False

  18. The area under any normal curve is equal to 1.
    a. True
    b. False

  19. In order to compute probabilities associated with a non-standard normal distribution, one must first convert to the standard normal distribution.
    a. True
    b. False

  20. The probability that the value of a normal random variable falls within one standard deviation of the mean is .5.
    a. True
    b. False

  21. If X is a normal random variable, then P(X = 2 0r x = -2) is approximately equal to 95%.
    a. True
    b. False

  22. The mode of a normal distribution is the point on the horizontal axis where the normal curve is highest.
    a. True
    b. False

  23. For any normal distribution, the square of the mean is equal to the product of the median and the mode.
    a. True
    b. False

  24. P(Z > 2.3) = P(Z < -2.3)
    a. True
    b. False

  25. As df gets large, the t distributions approach the standard normal distribution.
    a. True
    b. False

Copyright 2003 by Richard C. Weimer (rweimer@frostburg.edu)
Normal Distributions