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WGU C955 Probability and Statistics Objective
Assessment Exam (2026/2027) | Study Guide | Latest
Update 2026/2027 | Practice Questions and Answers |
Exam Review
Table of Contents
1. Descriptive Statistics: Measures of Center and Spread
2. Data Visualization and Interpretation
3. Probability Fundamentals
4. Conditional Probability and Independence
5. Discrete Probability Distributions: Binomial and Poisson
6. Continuous Probability Distributions: Uniform and Normal
7. Sampling Distributions and the Central Limit Theorem
8. Confidence Intervals
9. Hypothesis Testing: One-Sample Tests
10. Hypothesis Testing: Two-Sample Tests
11. Correlation and Linear Regression
12. Chi-Square Tests
13. Analysis of Variance (ANOVA)
14. Statistical Literacy and Study Design
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Question 1: Which measure of central tendency is most affected by extreme outliers?
A) Mean
B) Median
C) Mode
D) Range
Correct Answer: A) Mean
The mean is calculated by summing all values and dividing by the number of values, so
extreme outliers can significantly pull the mean in their direction. The median and mode
are resistant to outliers.
Question 2: For the data set {2, 4, 4, 6, 10}, what is the mean?
A) 4
B) 5.2
C) 6
D) 4.5
Correct Answer: B) 5.2
The mean is (2 + 4 + 4 + 6 + 10) / 5 = = 5.2.
Question 3: For the data set {2, 4, 4, 6, 10}, what is the median?
A) 4
B) 5.2
C) 6
D) 10
Correct Answer: A) 4
The median is the middle value when data is ordered. In {2, 4, 4, 6, 10}, the middle value is
4.
Question 4: For the data set {2, 4, 4, 6, 10}, what is the mode?
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A) 2
B) 4
C) 6
D) 10
Correct Answer: B) 4
The mode is the value that appears most frequently. In this data set, 4 appears twice, while
all other values appear once.
Question 5: For the data set {2, 4, 4, 6, 10}, what is the range?
A) 4
B) 6
C) 8
D) 10
Correct Answer: C) 8
The range is the maximum value minus the minimum value: 10 − 2 = 8.
Question 6: What is the variance of the data set {2, 4, 4, 6, 10}? (Use population
variance.)
A) 6.56
B) 7.2
C) 8.2
D) 5.2
Correct Answer: A) 6.56
Population variance = Σ(x − μ)² / N. The mean is 5.2. Deviations: (−3.2)² = 10.24, (−1.2)² =
1.44, (−1.2)² = 1.44, (0.8)² = 0.64, (4.8)² = 23.04. Sum = 36.8. Variance = 36. = 7.36.
Wait, let me recalculate: 10.24 + 1.44 + 1.44 + 0.64 + 23.04 = 36.8. 36.8/5 = 7.36. Hmm,
none of the options match. Let me check my work. The mean is 26/5 = 5.2. Deviations:
2−5.2 = −3.2, squared = 10.24. 4−5.2 = −1.2, squared = 1.44. 4−5.2 = −1.2, squared = 1.44.
6−5.2 = 0.8, squared = 0.64. 10−5.2 = 4.8, squared = 23.04. Sum = 36.8. 36.8/5 = 7.36. So
the correct answer should be 7.36. Let me adjust the options. The correct answer is 7.36, so
option B is closest. Let me revise: A) 6.56, B) 7.36, C) 8.2, D) 5.2. Correct answer is B)
7.36.
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Question 7: What is the standard deviation of the data set {2, 4, 4, 6, 10}? (Use
population standard deviation.)
A) 2.56
B) 2.71
C) 3.2
D) 2.0
Correct Answer: B) 2.71
Standard deviation = √variance = √7.36 ≈ 2.71.
Question 8: What is the interquartile range (IQR) of the data set {1, 3, 5, 7, 9, 11, 13}?
A) 6
B) 8
C) 10
D) 12
Correct Answer: B) 8
Q1 is the median of the lower half {1, 3, 5} = 3. Q3 is the median of the upper half {9, 11,
13} = 11. IQR = Q3 − Q1 = 11 − 3 = 8.
Question 9: In a box plot, what does the box represent?
A) The range
B) The interquartile range (IQR)
C) The mean
D) The standard deviation
Correct Answer: B) The interquartile range (IQR)
In a box plot, the box represents the interquartile range (IQR), which is the range between
the first quartile (Q1) and the third quartile (Q3). The line inside the box represents the
median.
Question 10: Which measure of spread is most resistant to outliers?
A) Range
B) Variance
WGU C955 Probability and Statistics Objective
Assessment Exam (2026/2027) | Study Guide | Latest
Update 2026/2027 | Practice Questions and Answers |
Exam Review
Table of Contents
1. Descriptive Statistics: Measures of Center and Spread
2. Data Visualization and Interpretation
3. Probability Fundamentals
4. Conditional Probability and Independence
5. Discrete Probability Distributions: Binomial and Poisson
6. Continuous Probability Distributions: Uniform and Normal
7. Sampling Distributions and the Central Limit Theorem
8. Confidence Intervals
9. Hypothesis Testing: One-Sample Tests
10. Hypothesis Testing: Two-Sample Tests
11. Correlation and Linear Regression
12. Chi-Square Tests
13. Analysis of Variance (ANOVA)
14. Statistical Literacy and Study Design
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Question 1: Which measure of central tendency is most affected by extreme outliers?
A) Mean
B) Median
C) Mode
D) Range
Correct Answer: A) Mean
The mean is calculated by summing all values and dividing by the number of values, so
extreme outliers can significantly pull the mean in their direction. The median and mode
are resistant to outliers.
Question 2: For the data set {2, 4, 4, 6, 10}, what is the mean?
A) 4
B) 5.2
C) 6
D) 4.5
Correct Answer: B) 5.2
The mean is (2 + 4 + 4 + 6 + 10) / 5 = = 5.2.
Question 3: For the data set {2, 4, 4, 6, 10}, what is the median?
A) 4
B) 5.2
C) 6
D) 10
Correct Answer: A) 4
The median is the middle value when data is ordered. In {2, 4, 4, 6, 10}, the middle value is
4.
Question 4: For the data set {2, 4, 4, 6, 10}, what is the mode?
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A) 2
B) 4
C) 6
D) 10
Correct Answer: B) 4
The mode is the value that appears most frequently. In this data set, 4 appears twice, while
all other values appear once.
Question 5: For the data set {2, 4, 4, 6, 10}, what is the range?
A) 4
B) 6
C) 8
D) 10
Correct Answer: C) 8
The range is the maximum value minus the minimum value: 10 − 2 = 8.
Question 6: What is the variance of the data set {2, 4, 4, 6, 10}? (Use population
variance.)
A) 6.56
B) 7.2
C) 8.2
D) 5.2
Correct Answer: A) 6.56
Population variance = Σ(x − μ)² / N. The mean is 5.2. Deviations: (−3.2)² = 10.24, (−1.2)² =
1.44, (−1.2)² = 1.44, (0.8)² = 0.64, (4.8)² = 23.04. Sum = 36.8. Variance = 36. = 7.36.
Wait, let me recalculate: 10.24 + 1.44 + 1.44 + 0.64 + 23.04 = 36.8. 36.8/5 = 7.36. Hmm,
none of the options match. Let me check my work. The mean is 26/5 = 5.2. Deviations:
2−5.2 = −3.2, squared = 10.24. 4−5.2 = −1.2, squared = 1.44. 4−5.2 = −1.2, squared = 1.44.
6−5.2 = 0.8, squared = 0.64. 10−5.2 = 4.8, squared = 23.04. Sum = 36.8. 36.8/5 = 7.36. So
the correct answer should be 7.36. Let me adjust the options. The correct answer is 7.36, so
option B is closest. Let me revise: A) 6.56, B) 7.36, C) 8.2, D) 5.2. Correct answer is B)
7.36.
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Question 7: What is the standard deviation of the data set {2, 4, 4, 6, 10}? (Use
population standard deviation.)
A) 2.56
B) 2.71
C) 3.2
D) 2.0
Correct Answer: B) 2.71
Standard deviation = √variance = √7.36 ≈ 2.71.
Question 8: What is the interquartile range (IQR) of the data set {1, 3, 5, 7, 9, 11, 13}?
A) 6
B) 8
C) 10
D) 12
Correct Answer: B) 8
Q1 is the median of the lower half {1, 3, 5} = 3. Q3 is the median of the upper half {9, 11,
13} = 11. IQR = Q3 − Q1 = 11 − 3 = 8.
Question 9: In a box plot, what does the box represent?
A) The range
B) The interquartile range (IQR)
C) The mean
D) The standard deviation
Correct Answer: B) The interquartile range (IQR)
In a box plot, the box represents the interquartile range (IQR), which is the range between
the first quartile (Q1) and the third quartile (Q3). The line inside the box represents the
median.
Question 10: Which measure of spread is most resistant to outliers?
A) Range
B) Variance
