Notation Assume that we want to find the probability that when five speaking characters in movies are randomly selected, exactly two of them are females. Also assume that when randomly selecting a speaking character in a movie, the probability of getting a female is 0.331. Identify the values of n, x, p, and q.
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 53m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 12m
- 9. Hypothesis Testing for One Sample2h 19m
- 10. Hypothesis Testing for Two Samples3h 22m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 20m
- 14. ANOVA1h 0m
5. Binomial Distribution & Discrete Random Variables
Binomial Distribution
Problem 5.2.7
Textbook Question
In Exercises 5–12, determine whether the given procedure results in a binomial distribution or a distribution that can be treated as binomial (by applying the 5% guideline for cumbersome calculations). For those that are not binomial and cannot be treated as binomial, identify at least one requirement that is not satisfied.
LOL In a U.S. Cellular survey of 500 smartphone users, subjects are asked if they find abbreviations (such as LOL or BFF) annoying, and each response was recorded as “yes,” “no,” or “not sure.”

1
Step 1: Recall the four requirements for a binomial distribution: (1) The procedure must have a fixed number of trials, (2) each trial must have only two possible outcomes (success or failure), (3) the trials must be independent, and (4) the probability of success must remain constant for all trials.
Step 2: Analyze the given problem. The survey involves 500 smartphone users, which represents a fixed number of trials. This satisfies the first requirement.
Step 3: Examine the possible outcomes for each trial. The responses are recorded as 'yes,' 'no,' or 'not sure,' which means there are three possible outcomes. This violates the second requirement, as a binomial distribution requires only two outcomes (e.g., success or failure).
Step 4: Since the second requirement is not satisfied, the procedure does not result in a binomial distribution. Additionally, the problem does not specify whether the trials are independent or whether the probability of success remains constant, but these are secondary considerations since the second requirement is already violated.
Step 5: Conclude that the given procedure does not result in a binomial distribution, and the primary reason is that there are more than two possible outcomes for each trial.

This video solution was recommended by our tutors as helpful for the problem above
Video duration:
4mPlay a video:
Was this helpful?
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Binomial Distribution
A binomial distribution models the number of successes in a fixed number of independent trials, each with the same probability of success. It requires two outcomes (success or failure), a fixed number of trials, and constant probability across trials. For example, flipping a coin multiple times and counting the number of heads is a classic binomial scenario.
Recommended video:
Guided course
Mean & Standard Deviation of Binomial Distribution
5% Guideline
The 5% guideline is a rule of thumb used to determine if a distribution can be treated as binomial when the sample size is large. It states that if the probability of success is less than 5% and the sample size is large, the trials can be considered independent, allowing for a binomial approximation. This is particularly useful in simplifying calculations for large datasets.
Requirements for Binomial Distribution
For a distribution to be classified as binomial, it must meet specific criteria: a fixed number of trials, only two possible outcomes per trial, independence of trials, and a constant probability of success. If any of these conditions are not met, the distribution may not be binomial. In the given survey, the presence of three response options (yes, no, not sure) violates the binary outcome requirement.
Recommended video:
Guided course
Mean & Standard Deviation of Binomial Distribution
Watch next
Master The Binomial Experiment with a bite sized video explanation from Patrick
Start learningRelated Videos
Related Practice
Textbook Question