MATH200 — Practice Quiz: Chapter 9 — 25 min

# Practice Quiz: Chapter 9

Work this like a regular quiz, using only your crib sheet. Give yourself a maximum of 25 minutes, then turn to the solutions and see how you did.

Show that requirements are met. You need not sketch the distribution, but write a sentence for each confidence interval.

Remember, you must show your work for full credit on any problems involving computation.

1(points: 5)  Lito-Fray was monitoring the percent salt content of batches of potato chips, and found the following results in a random sample of 11 batches:

1.6   1.4   1.6   0.9   1.3   1.4   1.5   1.4   1.2   1.3   1.7

Estimate the average salt content of all chips, by constructing a 95% confidence interval in endpoint form. Interpret your answer in English.

2(points: 1)  In World War II, a prisoner of war flipped a coin 10,000 times and recorded 5,067 heads. What number is the point estimate for proportion of heads?

3(points: 2½)  Last week, 42% of TV viewers watched American Idol. You wonder what percent will watch it this week. You want to be 90% confident of your answer, with a margin of error no greater than ±3.5%. How large must your random sample be?

4(points: 2½) You’re planning a study of vacation spending. From a past study, you have reason to believe that spending plans are normally distributed with σ = \$600. How many people will you need to ask, if you want a 98% confidence level and a margin of error no more than \$250?

5(points: 4)  You’ve read that two thirds of Americans believe in angels. You want to see whether that’s true at TC3, so you take a random sample of 100 TC3 students and you find that 61 of them believe in angels. Construct and interpret a 95% confidence interval about the proportion of all TC3 students who believe in angels.

Solutions to this practice quiz are available at http://www.tc3.edu/instruct/sbrown/stat/