Carmen Homework 9

For a normally distributed variable X with mean 40 and standard deviation 10, what is the probability that X equals exactly 30? In notation, what is P(X = 30)?

a. 0 b. 0.159 c. 0.841 d. .0242

Suppose X has a normal distribution with mean 10 and standard deviation 2. In order for the Z-score to be equal to 0, then X must be equal to

a. 0 b. 2 c. 10 d. None of these choices are correct

X is a normally distributed random variable with mean 50 and standard deviation 5. What is the probability that 2X will be less than 110?

a. 0.023 b. 0.159 c. 0.841 d. 0.977

If the Z-score is 1.96, and X has a normal distribution with mean 60 and standard deviation 6, what X-value corresponds to this Z-score?

a. 71.76 b. 67.96 c. 61.96 d. 48.24

The time (X) to complete a standardized exam is approximately normal with a mean of 70 minutes and standard deviation of 10 minutes. How much time should be given to complete the exam so that 80% of the students will complete the exam in the time given?

a. 84.7 minutes b. 78.4 minutes c. 92.3 minutes d. 74.8 minutes

Answer Sheet

1. c 2. d 3. a 4. b 5. a 6. b 7. b 8. a 9. d 10. c

If an observation has a Z-score of -1.5, how many standard deviations is it above or below the mean?

a. 1.5 standard deviations above the mean b. 0.066 standard deviations above the mean c. 0.066 standard deviations below the mean d. 1.5 standard deviations below the mean

The Normal distribution is an example of a ___________________ Distribution.

a. Continuous b. Discrete c. Neither

The time to complete a standardized exam is approximately normal with a mean of 70 minutes and a standard deviation of 10 minutes. The percentage of the students which take longer than 80 minutes to complete the exam is 84.13%.

a. True b. False

What is the probability that a normally distributed random variable X is greater than 85 if MU of X = 75 and SE of X = 4?

a. 1 b. 0.006 c. 0.994 d. 2.5

Where is the 10th percentile of the Z distribution?

a. 0.10 b. 0.90 c. 1.28 d. -1.28