MATH200 — Practice Quiz: Chapter 9 — 25 min
Practice Quiz: Chapter 9
Work this like a regular quiz, using only your crib
yourself a maximum of 25 minutes,
then turn to the
solutions and see how
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.
(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
1.6 1.4 1.6 0.9
1.3 1.4 1.5 1.4
1.2 1.3 1.7
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.
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Solutions to this practice quiz are available at