AP Statistics : Confidence and Proportion
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Example Questions
Example Question #2 : Confidence Intervals
Example Question #1 : Confidence Intervals
In a simple random sample of 
The sample is not sufficiently large. A confidence interval cannot be used.
Step 1: Determine the approporiate formula. In this case, the statistic is a proportion because the question says 261 people out of 1000 are left-handed. We want to use a confidence interval for proportions. The equation is
Step 2: 
Step 3: The questions asks for a 95% confidence interval. You can assume a normal distribution because of the large sample size. Therefore, in a normal distribution, 95% of the data is contained within 
Step 4: Substitue all the values into the equation to get the answer.
Example Question #11 : Confidence Intervals
A health insurance executive suspects that 50% of insurance applications are incomplete (i.e. critical data is missing from the application). He wants to gather a sample to estimate the true proportion. He wants to be within 5% of the true mean with 95% confidence.
What sample size does he need?
395
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