confidence intervals for a population mean

Review confidence intervals for a population mean for AP Statistics and try 2 free AP-style practice questions. 17 questions on this topic in AP Statistics · Unit 7 · Inference for Quantitative Data: Means.

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Question 1

A food technologist measures the fat content of 15 randomly selected portions of a salad dressing and finds a mean of 28.6 percent with a standard deviation of 3.1 percent. The label states that the dressing is 26 percent fat. Using $t^* = 2.145$ with 14 degrees of freedom, which of the following gives a 95 percent confidence interval for the mean fat content and a correct conclusion about the label?

Question 2

A road safety researcher measured the reaction times of a random sample of $n = 25$ drivers and used the data to construct a 95 percent confidence interval for the mean reaction time of all drivers in the population. The resulting interval is $(284, 316)$ milliseconds. Which of the following is the correct interpretation of this interval?

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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.

Question 13 / 4 pts

Part a1 / 1 pts

Point 1: Earned

94% sure

Reason: Correctly identifies demand for gasoline as inelastic.

Evidence: "The price of gasoline rises and the quantity falls only a little."

Part b2 / 3 pts

Point 1: Earned

91% sure

Reason: Graph shows relatively inelastic demand.

Evidence: Draws a steep demand curve.

Point 2: Earned

88% sure

Reason: Correct new equilibrium price.

Evidence: Shifts supply left, P1 → P2.

Point 3: Not earned

82% sure

Reason: With inelastic demand, a price increase raises total revenue.

Evidence: "Revenue goes down."

Confidence intervals for a population mean: AP Statistics Practice Questions | S&D Academy