An environmental scientist wants to construct a 95 percent confidence interval for the proportion of adults in a small town of 800 residents who own a bicycle, using a random sample of 90 adults from the town, of whom 27 owned a bicycle. Before proceeding, the environmental scientist checks the conditions for inference. Which of the following statements correctly identifies whether all conditions for constructing the interval are met?
justifying a claim based on a confidence interval for a population proportion
Review justifying a claim based on a confidence interval for a population proportion for AP Statistics and try 2 free AP-style practice questions. 17 questions on this topic in AP Statistics · Unit 3 · Inference for Categorical Data: Proportions.
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A journalist wants to estimate the proportion of all residents of a state who favor a proposed tax increase by surveying a random sample of 1,200 residents drawn from the state's 4.8 million residents. In the sample, 3.5 percent favored the tax increase. The journalist plans to construct a 95 percent confidence interval for the population proportion. Which of the following correctly evaluates whether the journalist can proceed as planned?
Sample free-response question
A town tests samples from its water supply. Each sample is either contaminated or not. The safe standard is that at most 5 percent of samples are contaminated. The town tests H0: p = 0.05 against Ha: p > 0.05 every month.
(a) Describe a Type I error and a Type II error in this context.
(b) Which error is more serious for the town's residents? Explain.
(c) Should the town use a significance level of 0.01 or 0.10? Explain using part (b).
(d) Describe two ways the town could increase the power of its test.
(e) The test has power 0.70 if the true rate is 8 percent. Interpret this value.
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Answer, then see why
The price of gasoline rises 10% and the quantity demanded falls 5%. What happens to total revenue?
Not quite. The answer is B.
Why the other options are wrong
AI grading for free-response
Write your FRQ answer and get it scored point by point against the AP rubric, with the line from your answer that earned or missed each point.
Reason: Correctly identifies demand for gasoline as inelastic.
Evidence: "The price of gasoline rises and the quantity falls only a little."
Reason: Graph shows relatively inelastic demand.
Evidence: Draws a steep demand curve.
Reason: Correct new equilibrium price.
Evidence: Shifts supply left, P1 → P2.
Reason: With inelastic demand, a price increase raises total revenue.
Evidence: "Revenue goes down."