Math Problem Statement
In a survey, 23 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $43 and standard deviation of $2. Find the margin of error at a 80% confidence level.
Give your answer to two decimal places.
Solution
To calculate the margin of error (ME) at an 80% confidence level, we use the following formula:
where:
- is the z-score corresponding to the 80% confidence level,
- is the standard deviation (which is 2 in this case),
- is the sample size (which is 23).
Step 1: Find the z-score for 80% confidence level.
For an 80% confidence level, the area in each tail of the standard normal distribution is . We look for the z-score corresponding to an area of 0.90 (i.e., 80% confidence in the middle).
From the standard normal table or a z-score calculator, the z-score for 80% confidence is approximately:
Step 2: Calculate the margin of error.
Now, we substitute the known values into the formula:
Step 3: Round the result.
Rounding to two decimal places:
So, the margin of error is approximately $0.53.
Do you want further details or have any questions on the calculation?
Here are 5 related questions to expand your understanding:
- How would the margin of error change if the confidence level were 95% instead of 80%?
- What would happen to the margin of error if the sample size were increased to 50?
- How does a larger standard deviation affect the margin of error?
- How can the margin of error be used to interpret the results of this survey?
- What is the difference between the margin of error and the standard error?
Tip: The margin of error helps to understand the precision of a sample statistic, and it's important to choose an appropriate confidence level for your analysis.
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Math Problem Analysis
Mathematical Concepts
Statistics
Confidence Intervals
Margin of Error
Formulas
ME = z × (σ / √n)
Theorems
Empirical Rule for Normal Distribution
Suitable Grade Level
Grades 11-12 or College Introductory Statistics
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