A study compares three fertilizer types on crop yield. A farmer has 30 plots of land of varying soil quality. A researcher randomly assigns 10 plots to each fertilizer type using random number assignment. Why is random assignment to plots important here, given that soil quality varies?
introduction to experimental design
Review introduction to experimental design for AP Statistics and try 2 free AP-style practice questions. 23 questions on this topic in AP Statistics · Unit 1 · Exploring One-Variable Data and Collecting Data.
9 topics174 multiple-choice8 free-response
Try free questions
A high school counselor wants to know whether a new after-school tutoring program improves students' scores on a standardized math test. Rather than randomly assigning students to treatment groups, she assigns all students who attend the morning study hall to the tutoring program and all students who attend the afternoon study hall to receive no tutoring. Suppose students who choose the morning session are, on average, substantially more academically motivated than those who choose the afternoon session. If motivation is confounded with tutoring assignment in this study, what is most likely true about the results?
Sample free-response question
A courier company recorded the delivery times, in minutes, for 10 randomly selected deliveries on each of two routes.
| Route | Delivery times (minutes) |
|---|---|
| North | 12, 15, 15, 16, 18, 19, 21, 22, 24, 38 |
| South | 14, 16, 17, 17, 18, 18, 19, 20, 20, 21 |
(a) Calculate the median delivery time for each route. Show your work.
(b) Is the North delivery time of 38 minutes an outlier? Justify your answer using the 1.5 x IQR rule. The North quartiles are Q1 = 15 and Q3 = 22.
(c) Compare the distributions of delivery times for the two routes. Address center and variability, in context.
(d) The company wants deliveries that rarely take a long time. Which route should it choose? Explain using the comparisons in part (c).
21 more questions on this topic
Full practice for AP Statistics · Unit 1 · Exploring One-Variable Data and Collecting Data: timed tests, step-by-step explanations for every answer, and AI grading for free-response questions.
Start practicing freeInside the course
How practice works on S&D Academy
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
Grader confidence 94% sureReason: 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
Grader confidence 91% sureReason: Graph shows relatively inelastic demand.
Evidence: Draws a steep demand curve.
Point 2: Earned
Grader confidence 88% sureReason: Correct new equilibrium price.
Evidence: Shifts supply left, P1 → P2.
Point 3: Not earned
Grader confidence 82% sureReason: With inelastic demand, a price increase raises total revenue.
Evidence: "Revenue goes down."