AP Statistics Review #4

1. Senior citizens make up about 13.4% of the American population. If a random sample of300 Americans is selected, what is the probability that more than 270 are NOT seniorcitizens.(A)(B)(C)(D)(E)

2. In the year’s county mathematics competition, a student scored 38; in last year’scompetition, the student scored 33. The average score this year was 36 with a standarddeviation of 2. Last year’s average score was 32 with a standard deviation of 1. In whichyear did the student score better?(A)The student scored better on this year’s exam.(B) The student scored better on last year’s exam.(C)The student scored equally well on both exams.(D)Without knowing the number of test items, it is impossible to determine the betterscore.(E) Without knowing the number of students taking the exam in the county, it isimpossible to determine the better score.

3. A newlywed couple is trying to choose one of two cities to start their new lives together.They randomly choose 20 cost of living factors, check their values for each city, thenconduct a test to determine if one city has a significantly lower cost of living than theother. What test should they conduct?(A)Two-sample z-test(B) Two-sample t-test(C)Matched-pairs t-test(D) ² goodness-of-fit test(E)Linear regression t-test

4. One hospital has 2000 live births during 2009, while a second hospital has 1000 birthsduring the same year.(a) Assuming there is a 50% chance for a live-born infant to be male, which hospital ismore likely to have less than 45% male births? Explain your answer.(b) Suppose the first hospital has 1030 male births, while the second has only 480. Is thedifference statistically significant? Show your work.

5. Drying times y (in minutes) are tabulated for various concentrations of pigment x (in grams perounce) for a certain brand of nail polish. A linear regression model givesy = -4.9x +62.3 with the following residual plot:5**0-5** ***xA nonlinear model gives y = -16.8 lnx + 59.8 with the following residual plot:0.3***0.3* * **(a) What does each model predict for the drying time when using 5 grams of pigment per ounce?(b) Which model is a better fit? Explain.