CHAPTER 6
- True or false questions.
- The probability that a standard normal random variable, Z, is between 1.50 and 2.10 is the same as the probability Z is between – 2.10 and – 1.50.
- The probability that a standard normal random variable, Z, is less than 50 is approximately 0.
- Theoretically, the mean, median, and the mode are all equal for a normal distribution.
- Any set of normally distributed data can be transformed to its standardized form.
- The “middle spread,” that is the middle 50% of the normal distribution, is equal to one standard deviation.
- Multiple choice questions.
- In its standardized form, the normal distribution
- has a mean of 0 and a standard deviation of 1.
- has a mean of 1 and a variance of 0.
- has an area equal to 0.5.
- cannot be used to approximate discrete probability distributions.
- Which of the following about the normal distribution is not true?
- Theoretically, the mean, median, and mode are the same.
- About 2/3 of the observations fall within 1 standard deviation from the mean.
- It is a discrete probability distribution.
- Its parameters are the mean, , and standard deviation, .
- If a particular batch of data is approximately normally distributed, we would find that approximately
- 2 of every 3 observations would fall between 1 standard deviation around the mean.
- 4 of every 5 observations would fall between 28 standard deviations around the mean.
- 19 of every 20 observations would fall between 2 standard deviations around the mean.
- b and c are correct.
- Solve the following problems in separate sheets of paper.
- The amount of pyridoxine (in grams) in a multiple vitamin is normally distributed with = 110 grams and = 25 grams.
(1) What is the probability that a randomly selected vitamin will contain between 100 and 110 grams of pyridoxine?
(2) What is the probability that a randomly selected vitamin will contain between 82 and 100 grams of pyridoxine?
(3) What is the probability that a randomly selected vitamin will contain at least 100 grams of pyridoxine?
(4)What is the probability that a randomly selected vitamin will contain between 100 and 120 grams of pyridoxine?
(5)What is the probability that a randomly selected vitamin will contain less than 100 grams of pyridoxine?
(6)What is the probability that a randomly selected vitamin will contain less than 100 grams or more than 120 grams of pyridoxine?
(7)Approximately 83% of the vitamins will have at least how many grams of pyridoxine?
Suppose Z has a standard normal distribution with a mean of 0 and standard deviation of 1.
(1) What is the probability that Z is less than 1.15?
(2)What is the probability that Z is more than 0.77?
(3) What is the probability that Z is less than -2.20?
(4)What is the probability that Z is more than -0.98?
(5)What is the probability that Z is between -2.33 and 2.33?
(6) What is the probability that Z is between -2.89 and -1.03?
- The amount of time necessary for assembly line workers to complete a product is a normal random variable with a mean of 15 minutes and a standard deviation of 2 minutes.
(1) What is the probability that a product is assembled in less than 12 minutes?
(2) What is the probability that a product is assembled in between 14 and 16 minutes?
(3) What is the probability that a product is assembled in between 10 and 12 minutes?
(4) What is the probability that a product is assembled in between 16 and 21 minutes?
(5) What is the probability that a product is assembled in more than 11 minutes?
(7) 15% of the products require more than __________ minutes for assembly.
(8) 90% of the products require more than __________ minutes for assembly.