A market research firm is studying customer satisfaction for a food delivery service. Based on past data, of customers rate the service as "satisfactory". The firm randomly surveys groups of 250 customers. Find the mean and standard deviation of the sampling distribution for . What would the shape of the sampling distribution be?
Table of contents
- 1. Introduction to Statistics53m
- 2. Describing Data with Tables and Graphs2h 1m
- 3. Describing Data Numerically1h 48m
- 4. Probability2h 26m
- 5. Binomial Distribution & Discrete Random Variables2h 55m
- 6. Normal Distribution & Continuous Random Variables1h 48m
- 7. Sampling Distributions & Confidence Intervals: Mean2h 8m
- 8. Sampling Distributions & Confidence Intervals: Proportion1h 20m
- 9. Hypothesis Testing for One Sample2h 23m
- 10. Hypothesis Testing for Two Samples3h 25m
- 11. Correlation1h 6m
- 12. Regression1h 4m
- 13. Chi-Square Tests & Goodness of Fit1h 30m
- 14. ANOVA1h 4m
8. Sampling Distributions & Confidence Intervals: Proportion
Sampling Distribution of Sample Proportion
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A previous study found that 80% of people preferred drinking Pepsi over Coca Cola. Use a normal distribution to approximate the probability that, from this same random sample of 100 people, that between 10 and 11 people prefer Coca Cola.
A
0.0125
B
0.9875
C
0.8
D
0.105

1
Identify the problem as a binomial distribution problem where the probability of success (preferring Coca Cola) is 0.2 (since 80% prefer Pepsi, 20% prefer Coca Cola).
Use the normal approximation to the binomial distribution. For a binomial distribution with parameters n (number of trials) and p (probability of success), the mean (μ) is given by μ = np and the standard deviation (σ) is given by σ = sqrt(np(1-p)).
Calculate the mean: μ = 100 * 0.2 = 20.
Calculate the standard deviation: σ = sqrt(100 * 0.2 * 0.8) = sqrt(16) = 4.
Convert the binomial problem to a normal distribution problem by finding the z-scores for 10 and 11 using the formula z = (X - μ) / σ, where X is the number of successes. Then, use the standard normal distribution to find the probability that the number of people preferring Coca Cola is between 10 and 11.
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