Table of contents
- 1. Intro to Stats and Collecting Data55m
- 2. Describing Data with Tables and Graphs1h 55m
- 3. Describing Data Numerically1h 45m
- 4. Probability2h 16m
- 5. Binomial Distribution & Discrete Random Variables2h 33m
- 6. Normal Distribution and Continuous Random Variables1h 38m
- 7. Sampling Distributions & Confidence Intervals: Mean1h 3m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample1h 1m
- 10. Hypothesis Testing for Two Samples2h 8m
- 11. Correlation48m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
4. Probability
Complements
Problem 6.CRE.4
Textbook Question
Blue Eyes Assume that 35% of us have blue eyes (based on a study by Dr. P. Soria at Indiana University).
b. Find the value of P(B_bar).

1
Step 1: Understand the problem. The problem involves finding the complement probability of the event B, where B represents the event that a person has blue eyes. The complement of an event, denoted as BÌ…, represents the event that a person does NOT have blue eyes.
Step 2: Recall the complement rule in probability. The complement rule states that the probability of the complement of an event is given by: P(BÌ…) = 1 - P(B).
Step 3: Identify the given probability. From the problem, we are told that P(B) = 0.35, which is the probability that a person has blue eyes.
Step 4: Substitute the given value into the complement rule formula. Using the formula P(BÌ…) = 1 - P(B), substitute P(B) = 0.35 to calculate P(BÌ…).
Step 5: Simplify the expression. Perform the subtraction to find the value of P(BÌ…), which represents the probability that a person does NOT have blue eyes.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Complementary Probability
Complementary probability refers to the likelihood of an event not occurring. If the probability of an event A happening is P(A), then the probability of A not happening, denoted as P(A'), is calculated as P(A') = 1 - P(A). In this case, if 35% of people have blue eyes, the probability of not having blue eyes is the complement of this percentage.
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Probability Notation
Probability notation is a standardized way to express the likelihood of events. In this context, P(B) represents the probability of event B occurring, while P(B_bar) or P(B') denotes the probability of event B not occurring. Understanding this notation is crucial for interpreting and solving probability problems accurately.
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Basic Probability Calculation
Basic probability calculation involves determining the likelihood of an event based on known data. For example, if 35% of a population has blue eyes, the calculation for the probability of not having blue eyes (P(B_bar)) involves subtracting the given percentage from 100%. This fundamental skill is essential for solving various statistical problems.
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