Deck 6: The Normal Probability Distribution

Question 1

i. Asymptotic means that the normal curve gets closer and closer to the X-axis but never actually touches it.
Ii) When referring to the normal probability function, there is not just one of them; there is a "family" of them.
Iii) Some normal probability distributions have equal arithmetic means, but their standard deviations may be different.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Answer 1

A

Question 2

i. The uniform probability distribution is symmetric about the mean and median. ii. The uniform probability distribution's shape is a rectangle.

Answer 2

A

Question 3

The upper and lower limits of a uniform probability distribution are

A) positive and negative infinity.
B) plus and minus three standard deviations.
C) 0 and 1.
D) the maximum and minimum values of the random variable.

Answer 3

D

Question 4

A financial advising company has determined that the price-to-earnings ratios for 20 randomly selected publicly traded companies range between 0.9 and 2.9. Given that the price-to-earnings ratios are uniformly distributed, what percent of price-to-earnings ratios are between 1.90 and 2.48?

A) 19%
B) 20%
C) 26%
D) 29%
E) None of the choices are correct

Question 5

The shape of any uniform probability distribution is

A) Negatively skewed
B) Positively skewed
C) Rectangular
D) Bell shaped

Question 6

What is an important similarity between the uniform and normal probability distributions?

A) The mean, median and mode are all equal.
B) The mean and median are equal.
C) They are negatively skewed.
D) About 68% of all observations are within one standard deviation of the mean.

Question 7

A major credit card company has determined that customers charge between $100 and $1,100 per month. Given that the average monthly amount charged is uniformly distributed, what percent of monthly charges are between $600 and $889?

A) 28.9%
B) 20.8%
C) 26.2%
D) 29.3%
E) None of the choices are correct

Question 8

Which of the following is true in a normal distribution?

A) Mean equals the mode and the median
B) Mode equals the median
C) Mean divides the distribution into two equal parts
D) All of the choices are correct
E) None of the choices are correct

Question 9

i. The normal curve falls off smoothly in either direction from the central value. Since it is asymptotic, the curve gets closer and closer to the X-axis, but never actually touches it.
ii. The mean (µ) divides the normal curve into two identical halves.
Iii) The number of different normal distributions is unlimited.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 10

A financial advising company has determined that the price-to-earnings ratios for 20 randomly selected publicly traded companies range between 0.9 and 2.9. Given that the price-to-earnings ratios are uniformly distributed, what is the average price-to-earnings ratio?

A) 0.9
B) 1.9
C) 2.9
D) 3.8
E) None of the choices are correct

Question 11

i. The Empirical Rule of probability can be applied to the uniform probability distribution.
ii. Areas within a continuous probability distribution represent probabilities.
iii. The total area within a continuous probability distribution is equal to 1.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 12

i. For any uniform probability distribution, the mean and standard deviation can be computed by knowing the maximum and minimum values of the random variable.
Ii) In a uniform probability distribution, P(x) is constant between the distribution's minimum and maximum values.
Iii) The uniform probability distribution's shape is a rectangle.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 13

i. The mean of a normal distribution is represented by ?.
ii. When referring to the normal probability function, there is not just one of them; there is a "family" of them.
Iii) Some normal probability distributions have equal arithmetic means, but their standard deviations may be different.

A) (i), (ii) and (iii) are all correct statements.
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false.

Question 14

i. The uniform probability distribution's standard deviation is proportional to the distribution's range.
ii. The uniform probability distribution is symmetric about the mode.
iii. For a uniform probability distribution, the probability of any event is equal to 1/(b-a).

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 15

i. Asymptotic means that the normal curve gets closer and closer to the X-axis but never actually touches it.
Ii) When referring to the normal probability function, there is not just one of them; there is a "family" of them.
Iii) Some normal probability distributions have different arithmetic means and different standard deviations.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 16

i. Areas within a continuous probability distribution represent probabilities.
ii. The Empirical Rule of probability can be applied to the uniform probability distribution.
iii. The total area within a continuous probability distribution is equal to 100.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 17

A major credit card company has determined that customers charge between $100 and $1,100 per month. Given that the average monthly amount charged is uniformly distributed, what is the probability that a person charges less than $200 per month?

A) 5%
B) 10%
C) 15%
D) 20%
E) None of the choices are correct

Question 18

The mean of any uniform probability distribution is

A) (b - a)/2
B) (a + b)/2
C)
D) nπ

Question 19

i. In a uniform probability distribution, P(x) is constant between the distribution's minimum and maximum values.
ii. For a uniform probability distribution, the probability of any event is equal to 1/(b-a).
iii. The uniform probability distribution is symmetric about the mode.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (ii) and, (iii) are correct statements but not (i).
E) All statements are false

Question 20

A major credit card company has determined that customers charge between $100 and $1,100 per month. Given that the average monthly amount charged is uniformly distributed, what is the standard deviation of the monthly amount charged?

A) 298.67
B) 275.57
C) 267.88
D) 288.67
E) None of the choices are correct

Question 21

Tables of normal distribution probabilities are found in many statistics books. These probabilities are calculated from a normal distribution with

A) a mean of 1 and a standard deviation of 1
B) a mean of 100 and a standard deviation of 15
C) a mean of 0 and a standard deviation of 15
D) a mean of 0 and a standard deviation of 1

Question 22

i. For a normal probability distribution, about 95 percent of the area under normal curve is within plus and minus two standard deviations of the mean and practically all (99.73 percent) of the area under the normal curve is within three standard deviations of the mean.
Ii) The total area under the normal curve is 100%.
Iii) The mean of a normal probability distribution is 500 and the standard deviation is 10. About 95 percent of the observations lie between 480 and 520.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (i) and, (ii) are correct statements but not (iii).
E) All statements are false

Question 23

Two business major students, in two different sections of economics, were comparing test scores. The following gives the students' scores, class mean, and standard deviation for each section. Which student scored better compared to the rest of their section?

A) The student in section A
B) The student in section B
C) Both students scored the same.
D) We are unable to determine who did better from the information given.

Question 24

Two competitive brothers, who work in two different industries, were comparing their salaries. Because there is a difference of 4 years in their respective work experience, they decided to compare, not their actual salaries, but to compare their salaries against their company averages to see who is doing better. The following gives the brothers' salaries, companies' mean, and standard deviation for each company. Which brother earns a higher salary compared to the rest of their colleagues?

A) Tom
B) Andy
C) They both compare the same when measured against their colleagues
D) Unable to determine from the information given

Question 25

Two competitive brothers, who work in two different industries, were comparing their salaries. Because there is a difference of 4 years in their respective work experience, they decided to compare, not their actual salaries, but to compare their salaries against their company averages to see who is doing better. The following gives the brothers' salaries, companies' mean, and standard deviation for each company. What is the z-score of Andy's salary?

A) -1.29
B) 1.29
C) -1.89
D) 1.89
E) None of the choices are correct.

Question 26

The mean of a normally distributed group of weekly incomes of a large group of executives is $1,000 and the standard deviation is $100. What is the z-score for an income of $1,100?

A) 1.00
B) 2.00
C) 1.683
D) -0.90
E) None of the choices are correct

Question 27

i. For a normal probability distribution, about 95 percent of the area under normal curve is within plus and minus two standard deviations of the mean and practically all (99.73 percent) of the area under the normal curve is within three standard deviations of the mean.
Ii) The total area under the normal curve is 1.
Iii) The mean of a normal probability distribution is 500 and the standard deviation is 10. About 68 percent of the observations lie between 480 and 520.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (i) and, (ii) are correct statements but not (iii).
E) All statements are false

Question 28

A random variable from an experiment where outcomes are normally distributed

A) can have any value between -σ and +σ
B) can have only a few discrete values
C) can have a mean of 0 and a standard deviation of 1
D) can have no values

Question 29

Two normal distributions are compared. One has a mean of 10 and a standard deviation of 10. The second normal distribution has a mean of 10 and a standard deviation of 2. Which of the following it true?

A) the locations of the distributions are different
B) the distributions are from two different families
C) the dispersions of the distributions are different
D) the dispersions of the distributions are the same

Question 30

Two competitive brothers, who work in two different industries, were comparing their salaries. Because there is a difference of 4 years in their respective work experience, they decided to compare, not their actual salaries, but to compare their salaries against their company averages to see who is doing better. The following gives the brothers' salaries, companies' mean, and standard deviation for each company. What is the z-score of Tom's salary?

A) -1.29
B) 1.29
C) -1.89
D) 1.89
E) None of the choices are correct.

Question 31

The total area of a normal probability distribution is

A) between -3.0 and 3.0.
B) 1.00.
C) dependent on a value of 'z'.
D) approximated by the binomial distribution.

Question 32

Which of the following is NOT a characteristic of the normal probability distribution?

A) Positively-skewed
B) Bell-shaped
C) Symmetrical
D) Asymptotic
E) All of the choices are correct

Question 33

i. In terms of a formula the standardized value of z is found by z = (X - µ)/σ.

Question 34

What is the distribution with a mean of 0 and a standard deviation of 1 called?

A) Frequency distribution
B) z-score
C) Standard normal distribution
D) Binomial probability distribution
E) None of the choices are correct

Question 35

i. A z-score is the distance between a selected value (X) and the population mean (μ) divided by the population standard deviation (σ).
Ii) The standard normal distribution is a special normal distribution with a mean of 0 and a standard deviation of 1.
Iii) A computed z for X values to the right of the mean is negative.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (i) and, (ii) are correct statements but not (iii).
E) All statements are false

Question 36

The standard normal probability distribution is one which has:

A) A mean of 1 and any standard deviation
B) Any mean and a standard deviation of 1
C) A mean of 0 and any standard deviation
D) A mean of 0 and a standard deviation of 1
E) None of the choices are correct are correct

Question 37

i. In terms of a formula the standardized value of z is found by z = (X - µ)/?.
ii. The standard normal distribution is a special normal distribution with a mean of 0 and a standard deviation of 1.
Iii) A computed z for X values to the right of the mean is positive.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (i) and, (ii) are correct statements but not (iii).
E) All statements are false

Question 38

Which of the following is NOT true regarding the normal distribution?

A) Mean, median and mode are all equal
B) It has a single peak
C) It is symmetrical
D) The points of the curve meet the X-axis at z = -3 and z = 3
E) None of the choices are correct

Question 39

i. Disaster Airlines determined that the mean number of passengers per flight is 152 with a standard deviation of ten passengers. Practically all flights have between 142 and 162 passengers.
ii. The total area under the normal curve is less than 1.
Iii) The mean of a normal probability distribution is 500 and the standard deviation is 10. About 68 percent of the observations lie between 480 and 520.

A) (i), (ii) and (iii) are all correct statements
B) (i) is a correct statement but not (ii) or (iii).
C) (i) and, (iii) are correct statements but not (ii).
D) (i) and, (ii) are correct statements but not (iii).
E) All statements are false

Question 40

For the normal distribution, the mean plus and minus 1.96 standard deviations will include about what percent of the observations?

A) 50%
B) 99.7%
C) 95%
D) 68%
E) None of the choices are correct

Question 41

The mean amount of gasoline and services charged by Key Refining Company credit customers is $70 per month. The distribution of amounts spent is approximately normal with a standard deviation of
$10) What is the probability of selecting a credit card customer at random and finding the customer charged between $70 and $83?

A) 0.1962
B) 0.4032
C) 0.3413
D) 0.4750
E) None of the choices are correct

Question 42

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. How many students earned between $45,000 and $53,000?

A) 170
B) 273
C) 334
D) 387
E) None of the choices are correct

Question 43

The mean of a normal probability distribution is 500 and the standard deviation is 10. About 95 percent of the observations lie between what two values?

A) 475 and 525
B) 480 and 520
C) 400 and 600
D) 350 and 650
E) None of the choices are correct

Question 44

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. How many students earned between
$47,000 and $53,000?

A) 137
B) 273
C) 113
D) 387
E) None of the choices are correct

Question 45

What is the area under the normal curve between z = -1.0 and z = -2.0?

A) 0.0228
B) 0.3413
C) 0.1359
D) 0.4772
E) None of the choices are correct

Question 46

The employees of Cartwright Manufacturing are awarded efficiency ratings. The distribution of the ratings approximates a normal distribution. The mean is 400, the standard deviation 50. What is the area under the normal curve between 400 and 482?

A) 0.5000
B) 0.4495
C) 0.3413
D) 0.4750
E) None of the choices are correct

Question 47

A new extended-life light bulb has an average service life of 750 hours, with a standard deviation of 50 hours. If the service life of these light bulbs approximates a normal distribution, about what percent of the distribution will be between 600 hours and 900 hours?

A) 95%
B) 68%
C) 34%
D) 99.7%
E) None of the choices are correct

Question 48

An accelerated life test on a large number of type-D alkaline batteries revealed that the mean life for a particular use before they failed is 19.0 hours. The distribution of the lives approximated a normal distribution. The standard deviation of the distribution was 1.2 hours. About 95.44 percent of the batteries failed between what two values?

A) 8.9 and 18.9
B) 12.2 and 14.2
C) 14.1 and 22.1
D) 16.6 and 21.4
E) None of the choices are correct

Question 49

What is the proportion of the total area under the normal curve within plus and minus two standard deviations of the mean?

A) 68%
B) 99.7%
C) 34%
D) 95%
E) None of the choices are correct are correct

Question 50

The mean amount spent by a family of four on food per month is $500 with a standard deviation of $75. Assuming that the food costs are normally distributed, what is the probability that a family spends less than $410 per month?

A) 0.2158
B) 0.8750
C) 0.0362
D) 0.1151
E) None of the choices are correct

Question 51

The seasonal output of a new experimental strain of pepper plants was carefully weighed. The mean weight per plant is 15.0 pounds, and the standard deviation of the normally distributed weights is 1.75 pounds. Of the 200 plants in the experiment, how many produced peppers weighing between 13 and
16 pounds?

A) 100
B) 118
C) 197
D) 53
E) None of the choices are correct

Question 52

The mean of a normal distribution is 400 kg. The standard deviation is 10 kg. What is the area between 415 kg and the mean of 400 kg?

A) 0.5000
B) 0.1932
C) 0.4332
D) 0.3413
E) None of the choices are correct

Question 53

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. How many students earned less than
$45,000?

A) 53
B) 197
C) 303
D) 35
E) None of the choices are correct

Question 54

For a standard normal distribution, what is the probability that z is greater than 1.75?

A) 0.0401
B) 0.0459
C) 0.4599
D) 0.9599
E) None of the choices are correct

Question 55

What is the area under the normal curve between z = 0.0 and z = 2.0?

A) 1.0000
B) 0.7408
C) 0.1359
D) 0.4772
E) None of the choices are correct

Question 56

The distribution of the annual incomes of a group of middle management employees approximated a normal distribution with a mean of $37,200 and a standard deviation of $800. About 68 percent of the incomes lie between what two incomes?

A) $30,000 and $40,000
B) $36,400 and $38,000
C) $34,800 and $39,600
D) $35,600 and $38,800
E) None of the choices are correct

Question 57

What is the area under the normal curve between z = 0.0 and z = 1.79?

A) 0.4633
B) 0.0367
C) 0.9599
D) 0.0401
E) None of the choices are correct

Question 58

The annual commissions per salesperson employed by a manufacturer of light machinery averaged $40,000 with a standard deviation of $5,000. What percent of the sales persons earn between $32,000 and $42,000?

A) 60.06%
B) 39.94%
C) 34.13%
D) 81.66%
E) None of the choices are correct

Question 59

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. How many students earned more than $55,000?

A) 53
B) 197
C) 303
D) 35
E) None of the choices are correct

Question 60

A national manufacturer of unattached garages discovered that the distribution of the lengths of time it takes two construction workers to erect the Red Barn model is approximately normally distributed with a mean of 32 hours and a standard deviation of 2 hours. What percent of the garages take between 32 and 34 hours to erect?

A) 16.29%
B) 76.71%
C) 3.14%
D) 34.13%
E) None of the choices are correct

Question 61

The average score of 100 students taking a statistics final was 70 with a standard deviation of 7. Assuming a normal distribution, approximately how many scored greater than 65?

A) 0.2611
B) 0.2389
C) 0.7611
D) D)-0.714
E) None of the choices are correct

Question 62

Suppose a tire manufacturer wants to set a mileage guarantee on its new XB 70 tire. Life test revealed that the mean mileage is 47,900 and the standard deviation of the normally distributed distribution of mileage is 2,050 miles. The manufacturer wants to set the guaranteed mileage so that no more than
5 percent of the tires will have to be replaced. What guaranteed mileage should the manufacturer
Announce?

A) 44,528
B) 32,960
C) 49,621
D) 40,922
E) None of the choices are correct

Question 63

The weights of cans of fruit are normally distributed with a mean of 1,000 grams and a standard deviation of 50 grams. What percent of the cans weigh 860 grams or less?

A) 0.0100
B) 0.8400
C) 0.0026
D) 0.0001
E) None of the choices are correct

Question 64

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. What is the income that separates the top 5% from the lower 95% of the incomes?

A) $43,420
B) $47,320
C) $56,580
D) $52,680
E) None of the choices are correct

Question 65

For the standard normal distribution, what z-score corresponds with the 85% percentile?

A) 0.30
B) 2.05
C) 0.15
D) 1.04
E) None of the choices are correct

Question 66

The net profit from a certain investment is normally distributed with a mean of $10,000 and a standard deviation of $5,000. The probability that the investor will have a net loss is

A) 0.4772
B) 0.9544
C) 0.0228
D) 0.9772
E) 1.0

Question 67

015 litres. What is the probability a container will have less than 2 litres?

A) 0.0918
B) 0.3413
C) 0.1926
D) 0.8741
E) None of the choices are correct

Question 68

An analysis of the grades on the first test in History 101 revealed that they approximate a normal curve with a mean of 75 and a standard deviation of 8. The instructor wants to award the grade of A to the upper 10 percent of the test grades. What is the dividing point between an A and a B grade?

A) 80
B) 85
C) 90
D) 95
E) None of the choices are correct

Question 69

A study of a company's practice regarding the payment of invoices revealed that on the average an invoice was paid 20 days after it was received. The standard deviation equalled five days. Assuming that the distribution is normal, what percent of the invoices were paid within 15 days of receipt?

A) 15.87%
B) 37.91%
C) 34.13%
D) 86.74%
E) None of the choices are correct

Question 70

The net profit from a certain investment is normally distributed with a mean of $10,000 and a standard deviation of $5,000. The probability that the investor will not have a net loss is:

A) 0.4772
B) 0.9544
C) 0.0228
D) 0.9772
E) 1.0

Question 71

The average score of 100 students taking a statistics final was 70 with a standard deviation of 7. Assuming a normal distribution, approximately how many scored less than 60?

A) 0.2271
B) 0.3729
C) 0.8929
D) D)-1.14
E) None of the choices are correct

Question 72

A statistics student receives a grade of 85 on a statistics midterm. If the corresponding z-score equals +1.5 and the standard deviation equals 7, the average grade on this exam is .

A) 74.5
B) 75.4
C) 68.5
D) 76.9
E) None of the choices are correct

Question 73

Management is considering adopting a bonus system to increase production. One suggestion is to pay a bonus on the highest 5 percent of production based on past experience. Past records indicate that, on the average, 4,000 units of a small assembly are produced during a week. The distribution of the weekly production is approximately normally distributed with a standard deviation of 60 units. If the bonus is paid on the upper 5 percent of production, the bonus will be paid on how many units or more?

A) 6,255
B) 5,120
C) 3,196
D) 4,099
E) None of the choices are correct

Question 74

Ball-Bearings, Inc. produces ball bearings automatically on a Kronar BBX machine. For one of the ball bearings, the mean diameter is set at 20.00 mm (millimetres). The standard deviation of the production over a long period of time was computed to be 0.150 mm. What percent of the ball bearings will have diameters 20.27 mm or more?

A) 41.00%
B) 12.62%
C) 3.59%
D) 85.00%
E) None of the choices are correct

Question 75

The average score of 100 students taking a statistics final was 70 with a standard deviation of 7. Assuming a normal distribution, approximately how many scored 90 or higher?

A) 0.4979
B) 0.0021
C) 0.9979
D) 2.86
E) None of the choices are correct

Question 76

A sample of 500 evening students revealed that their annual incomes were normally distributed with a mean income of $50,000 and a standard deviation of $4,000. What is the income that separates the top
25% from the lower 75% of the incomes?

A) $2,680
B) $47,320
C) $50,000
D) $52,680
E) None of the choices are correct

Question 77

The driver's seat in most vehicles is set to comfortably fit a person who is at least 159 cm tall. The distribution of heights of adult women is approximately normal with a mean of 161.5 cm and a standard deviation of 6.3 cm. Determine the percentage of women who can be expected to be uncomfortable in the driver's seat of their car without some sort of an adjustment.

A) 0.3446.
B) 0.1554.
C) 0.6554.
D) 0.8446
E) None of the choices are correct.

Question 78

The weekly mean income of a group of executives is $1,000 and the standard deviation of this group is $100. The distribution is normal. What percent of the executives have an income of $925 or less?

A) About 15%
B) About 85%
C) About 50%
D) About 23%
E) None of the choices are correct

Question 79

Past experience of a large manufacturing firm with administering a test to recent college graduates who had applied for a job revealed that the mean test score was 500, and the standard deviation was 50. The distribution of the test scores was normal. Based on this experience, management is considering placing a person whose score is in the upper 6 percent of the distribution directly into a responsible position. What is the lowest score a college graduate must earn to qualify for a responsible position?

A) 50
B) 625
C) 460
D) 578
E) None of the choices are correct

Question 80

The mean score of a college entrance test is 500; the standard deviation is 75. The scores are normally distributed. What percent of the students scored below 320?

A) About 50.82%
B) About 34.13%
C) About 7.86%
D) About 0.82%
E) None of the choices are correct