Statistics Help - Multiple Choice questions

A. 2

B. 3

C. 4

D. 4.1

Question 3 of 20

A study of the amount of time it takes a mechanic to rebuild the transmission for a 1992 Chevrolet Cavalier shows that the mean is 8.4 hours and the standard deviation is 1.77 hours. Assume that a random sample of 40 mechanics is selected and the mean rebuild time of the sample is computed. Assuming the mean times are normally distributed, what percentage of sample means are greater than 7.7 hours?

A. 0.62%

B. 34.46%

C. 65.54%

D. 99.38%

Question 4 of 20

Decide which of the described variables likely have a normal or near-normal distribution.

a) The amount of change held by a teacher at the end of each day for a year

b) The amount of pocket money held by each student at a mid-sized liberal arts college at a given time

c) The number of heads that show when two coins are tossed

A. a

B. b

C. c

D. None

Question 5 of 20

The lifetimes of projector bulbs of a particular type are normally distributed with a mean of 470 hours and a standard deviation of 15 hours. What percentage of the bulbs has lifetimes that lie within 2 standard deviations of the mean on either side?

Apply the 68-95-99.7 rule to this question.

A. 68%

B. 99.7%

C. 95%

D. 100%

Question 6 of 20

The annual precipitation amounts in a certain mountain range are normally distributed with a mean of 88 inches, and a standard deviation of 10 inches. What is the likelihood that the mean annual precipitation during 25 randomly picked years will be less than 90.8 inches?

A. 0.4192

B. 0.5808

C. 0.0808

D. 0.9192

Question 7 of 20

The amount of Jen’s monthly electric bill is normally distributed with a mean of $160 and a standard deviation of $14. Fill in the blanks.

95% of her electric bills are between __________ and __________.

Apply the 68-95-99.7 rule to this question.

A. $140, $190

B. $132, $190

C. $140, $188

D. $132, $188

Question 8 of 20

If light bulbs have lives that are normally distributed with a mean of 2500 hours and a standard deviation of 500 hours, use the 68-95-99.7 rule to approximate the percentage of light bulbs having a life between 2000 hours and 3500 hours?

A. About 13.5%

B. About 50%

C. About 68%

D. About 81.5%

Question 9 of 20

If light bulbs have lives that are normally distributed with a mean of 2500 hours and a standard deviation of 500 hours, approximately what percentage of light bulbs has a life of more than 3000 hours?

A. About 84%

B. About 68%

C. About 32%

D. About 16%

Question 10 of 20

The diameters of pencils produced by a certain machine are normally distributed with a mean of 0.30 inches and a standard deviation of 0.01 inches. In a random sample of 460 pencils, approximately how many would you expect to have a diameter less than 0.293 inches?

A. 123

B. 118

C. 112

D. 111

Question 11 of 20

A final exam in Math 160 has a mean of 73 with standard deviation 7.73. Assume that a random sample of 24 students is selected and the mean test score of the sample is computed. What percentage of sample means are less than 70?

A. 19.46%

B. 12.85%

C. 2.87%

D. 13.46%

Question 12 of 20

Which of the following statements concerning the standard normal curve is/are true (if any)?

a) The area under the standard normal curve to the left of -3 is zero.

b) The area under the standard normal curve between any two z-scores is greater than zero.

c) The area under the standard normal curve between two z-scores will be negative if both z-scores are negative.

d) The area under the standard normal curve to the left of any z-score is less than 1.

A. a, b

B. b, d

C. a, c

D. a

Question 13 of 20

The scores on a certain test are normally distributed with a mean score of 58 and a standard deviation of 4. What is the likelihood that a sample of 90 students will have a mean score of at least 58.4216?

A. 0.8413

B. 0.3413

C. 0.3174

D. 0.1587

Question 14 of 20

Which of the following statements concerning areas under the standard normal curve is/are true?

a) If a z-score is negative, the area to its right is greater than 0.5.

b) If the area to the right of a z-score is less than 0.5, the z-score is negative.

c) If a z-score is positive, the area to its left is less than 0.5.

A. a, c

B. b, c

C. a, b

D. a

Question 15 of 20

The diameters of bolts produced by a certain machine are normally distributed with a mean of 0.25 inches and a standard deviation of 0.01 inches. What percentage of bolts will have a diameter greater than 0.24 inches?

A. 79.13%

B. 82.46%

C. 84.13%

D. 84.46%

Question 16 of 20

The annual precipitation for one city is normally distributed with a mean of 72 inches and a standard deviation of 3.5 inches. Fill in the blanks.

In 99.7% of the years, the precipitation in this city is between __________ and __________ inches.

Apply the 68-95-99.7 rule to this questions.

A. 61.5, 82. 5

B. 82.5, 61.5

C. 61.5, 85.5

D. 63.5, 82.5

Question 17 of 20

If light bulbs have lives that are normally distributed with a mean of

2500 hours and a standard deviation of 500 hours, what percentage of

light bulbs have a life less than 2500 hours?

A. About 25%

B. About 50%

C. About 75%

D. About 68%

Question 18 of 20

Decide which of the described variables is/are likely to have a normal or near-normal distribution.

a) The heights of corn stalks in one row of corn that is half a mile long

b) The numbers of viewers of each of the channels from 202 to 550 on Direct TV at 7:00 PM CDT on the third Thursday of November 2012 (349 data values)

A. a

B. b

C. a and b

D. neither

Question 19 of 20

The amount of Jen’s monthly phone bill is normally distributed with a mean of $50 and a standard deviation of $10. Find the 25th percentile.

A. About $46.30

B. About $43.30

C. About $43.40

D. about $43.20

Question 20 of 20

The lifetimes of light bulbs of a particular type are normally distributed with a mean of 270 hours and a standard deviation of 11 hours. What percentage of the bulbs has lifetimes that lie within 2 standard deviations of the mean on either side?

Apply the 68-95-99.7 rule to this questions.

A. 68%

B. 1005

C. 99.7%

D. 95%