Deck 9: The Normal Distribution

Question 1

Use the 68-95-99.7 Rule to find probabilities or cutoff values.
Based on data collected from its production processes, Crosstiles Inc. determines that
The breaking strength of its most popular porcelain tile is normally distributed with a
Mean of 400 pounds per square inch and a standard deviation of 12.5 pounds per square
Inch. Based on the 68-95-99.7 Rule, about what percent of its popular porcelain tile will
Have breaking strengths between 375 and 425 pounds per square inch?

A) 95%
B) 68%
C) 84%
D) 32%
E) 47.5%

Answer 1

A

Question 2

Use the Normal model.
At a local manufacturing plant, employees must complete new machine set ups within
30 minutes. New machine set-up times can be described by a normal model with a mean
Of 22 minutes and a standard deviation of four minutes. The typical worker needs five
Minutes to adjust to his or her surroundings before beginning duties. What percent of
New machine set ups are completed within 25 minutes to allow for this?

A) 77.3%
B) 27.3%
C) 22.7%
D) 72.7%
E) none of the above

Answer 2

A

Question 3

Use the 68-95-99.7 Rule to find probabilities or cutoff values.
The time it takes to process phone orders in a small florist / gift shop is normally
Distributed with a mean of 6 minutes and a standard deviation of 1.24 minutes. What
Cutoff values would separate the 16% of orders that take the least time to process?

A) 3.52 minutes
B) 4.76 minutes
C) 8.48 minutes
D) 10.01 minutes
E) 11.98 minutes

Answer 3

B

Question 4

Use the Normal model.
A small flower shop takes orders by phone and then one of the staff florists is assigned
To prepare the arrangement. The time it takes to process phone orders is normally
Distributed with a mean of 6 minutes and a standard deviation of 2.5 minutes. The time it
Takes for an arrangement to be completed is normally distributed with a mean of 35
Minutes and a standard deviation of 8.6 minutes. What is the probability that it will take
More than 50 minutes to process a phone order and complete the floral arrangement at
This flower shop?

A) 0.8413
B) 0.3413
C) 0.2167
D) 0.1587
E) 0.6843

Question 5

Use the appropriate probability model (Exponential).
On weekdays from 11: 30 am to 2:00 pm customers arrive at a hotdog street vendor at the rate of 25 per 30 minute interval. Assume that this process can be well modeled by
The Poisson distribution. What is the probability that the vendor will have to wait at least
3 minutes for a customer?

A) 0.9179
B) 0.6734
C) 0.0821
D) 0.3912
E) 0.8854

Question 6

Use the appropriate probability model (Uniform).
Suppose that the time for e-mail confirmation of an online purchase is uniformly
Distributed between 1 and 6 minutes. What is the average time for an e-mail
Confirmation?

A) 3 minutes
B) 4 / minutes
C) 2.5 minutes
D) 4.5 minutes
E) 3.5 minutes

Question 7

Use the appropriate probability model (Exponential).
On weekdays from 11: 30 am to 2:00 pm customers arrive at a hotdog street vendor at the rate of 25 per 30 minute interval. Assume that this process can be well modeled by
The Poisson distribution. What is the average time between customer arrivals?

A) 1.2 minutes
B) 0.833 minutes
C) 25 minutes
D) 0.04 minutes
E) 2 minutes

Question 8

Use the Normal model to approximate the Binomial.
The unemployment rate of persons with a disability is typically higher than for those
With no disability. Recent statistics report that this rate is 14.5%. An advocacy group in
A large city located in the southeastern region of the U.S. selected a random sample of
250 persons with a disability. What is the probability that at least 20 persons in this
Sample are unemployed?

A) 0.8686
B) 0.9982
C) 0.6573
D) 0.1314
E) 0.0018

Question 9

Use the Normal model.
A company's manufacturing process uses 500 gallons of water at a time. A
"scrubbing" machine then removes most of a chemical pollutant before pumping the
Water into a nearby lake. To meet federal regulations the treated water must not contain
More than 80 parts per million (ppm) of the chemical. Because a fine is charged if
Regulations are not met, the company sets the machine to attain an average of 75 ppm in
The treated water. The machine's output can be described by a normal model with
Standard deviation 4.2 ppm. What percent of the batches of water discharged exceed the
80 ppm standard?

A) 11.7%
B) 1.17%
C) 88.3%
D) 8.83%
E) 3.89%

Question 10

Use the Normal model.
A company's manufacturing process uses 500 gallons of water at a time. A
"scrubbing" machine then removes most of a chemical pollutant before pumping the
Water into a nearby lake. To meet federal regulations the treated water must not contain
More than 80 parts per million (ppm.) of the chemical. The machine's output can be
Described by a normal model with standard deviation 4.2 ppm. The company's lawyers
Insist that not more than 2% of the treated water should be over the limit. To achieve
This, to what mean should the company set the scrubbing machine?

A) 80 ppm.
B) 75 ppm.
C) 71.374 ppm.
D) 88.626 ppm.
E) 69.459 ppm.

Question 11

Use the 68-95-99.7 Rule to find probabilities or cutoff values.
The time it takes to process phone orders in a small florist / gift shop is normally
Distributed with a mean of 6 minutes and a standard deviation of 1.24 minutes. What
Cutoff value would separate the 2.5% of orders that take the most time to process?

A) 3.52 minutes
B) 4.76 minutes
C) 8.48 minutes
D) 10.01 minutes
E) 11.98 minutes

Question 12

Use the Normal model to approximate the Binomial.
According to the Census Bureau, 68% of Americans owned their own home in 2003.
A local real estate office wants to see if this is the case for its area. The office selects a
Random sample of 200 people to estimate the percentage who own their own homes.
What is the probability that at least 140 people own their own home?

A) 0.7291
B) 0.2709
C) 0.4598
D) 0.5402
E) 0.1299

Question 13

The time it takes to process phone orders in a small florist / gift shop is normally
distributed with a mean of 6 minutes and a standard deviation of 1.24 minutes.
a. What cutoff value would separate the 2.5% of orders that take the most time to
process?
b. What cutoff value would separate the 16% of orders that take the least time to process?
c. What cutoff values would separate the 95% of orders that are in the middle of the
distribution with respect to processing time?

Question 14

Use the Normal model to approximate the Binomial.
The unemployment rate of persons with a disability is typically higher than for those
With no disability. Recent statistics report that this rate is 14.5%. An advocacy group in
A large city located in the southeastern region of the U.S. selected a random sample of
250 persons with a disability. What is the probability that no more than 30 persons in this
Sample are unemployed?

A) 0.8686
B) 0.9982
C) 0.6573
D) 0.1314
E) 0.0018

Question 15

Use the Normal model to approximate the Binomial.
According to the Census Bureau, 68% of Americans owned their own home in 2003.
A local real estate office wants to see if this is the case for its area. The office selects a
Random sample of 200 people to estimate the percentage who own their own homes. The
Standard deviation of the Normal model used to approximate this distribution is

A) 136
B) 64
C) 43.52
D) 6.597
E) 2.365

Question 16

Use the Normal model.
A small flower shop takes orders by phone and then one of the staff florists is assigned
To prepare the arrangement. The time it takes to process phone orders is normally
Distributed with a mean of 6 minutes and a standard deviation of 2.5 minutes. The time it
Takes for an arrangement to be completed is normally distributed with a mean of 35
Minutes and a standard deviation of 8.6 minutes. What is the standard deviation for the
Total time to process a phone order and complete the floral arrangement at this flower
Shop (assuming times are independent)?

A) 8.96 minutes
B) 41 minutes
C) 80.28 minutes2
D) 4.87 minutes
E) 12.43 minutes

Question 17

Use the 68-95-99.7 Rule to find probabilities or cutoff values.
Based on data collected from its production processes, Crosstiles Inc. determines that
The breaking strength of its most popular porcelain tile is normally distributed with a
Mean of 400 pounds per square inch and a standard deviation of 12.5 pounds per square
Inch. Based on the 68-95-99.7 Rule, about what percent of its popular porcelain tile will
Have breaking strengths greater than 412.5 pounds per square inch?

A) 95%
B) 68%
C) 16%
D) 32%
E) 47.5%

Question 18

Use the Normal model.
At a local manufacturing plant, employees must complete new machine set ups within
30 minutes. New machine set-up times can be described by a normal model with a mean
Of 22 minutes and a standard deviation of four minutes. What percent of new machine
Set ups take more than 30 minutes?

A) 97.72%
B) 47.72%
C) 2.28%
D) 52.28%
E) none of the above

Question 19

Use the appropriate probability model (Uniform).
Suppose that the time for e-mail confirmation of an online purchase is uniformly
Distributed between 1 and 6 minutes. The probability that an e-mail confirmation arrives
Within 3 minutes is

A) 0.50
B) 0.40
C) 0.60
D) 0.80
E) 0.10

Question 20

Use the appropriate probability model (Uniform).
Suppose the time it takes for customer representatives to diagnose and fix computer
Problems is uniformly distributed from 10 to 120 minutes. What is the probability that a
Problem is diagnosed and fixed within 30 minutes?

A) 0.27
B) 0.73
C) 0.82
D) 0.50
E) 0.18

Question 21

Use the appropriate probability model (Uniform).
Suppose the time it takes for customer representatives to diagnose and fix computer
Problems is uniformly distributed from 10 to 120 minutes. What is the probability that it
Takes longer than 90 minutes to diagnose and fix a computer problem?

A) 0.27
B) 0.73
C) 0.82
D) 0.50
E) 0.18