91影视

High tuition costs Glenn wonders what proportion of the students at his school think that tuition is too high. He interviews an SRS of $50$ of the $2400$ students at his college. Thirty-eight of those interviewed think tuition is too high.

AIDS and risk factors In the National AIDS

Behavioral Surveys sample of $2673$adult heterosexuals, $0.2\%$had both received a blood transfusion and had a sexual partner from a group at high risk of A I D S. We want to estimate the proportion $p$in the population who share these two risk factors.

Going to the prom Tonya wants to estimate what proportion of the seniors in her school plan to attend the prom. She interviews an SRS of $50$ of the $750$ seniors in her school and finds that $36$ plan to go to the prom

Whelks and mussels The small round holes you often see in sea shells were drilled by other sea creatures, who ate the former dwellers of the shells. Whelks often drill into mussels, but this behavior appears to be more or less common in different locations. Researchers collected whelk eggs from the coast of Oregon, raised the whelks in the laboratory, then put each whelk in a container with some delicious mussels. Only $9of98$whelks drilled into a mussel. The researchers want to estimate the proportion $p$ of Oregon whelks that will spontaneously drill into mussels.

98% Confidence find $z^{*}$for a$98\%$confidence interval using table A or tour calculator. show your method.

Define the parameter of interest.

$93\%$ confidence Find $z*fora93\%$confidence interval using Table A or your calculator. Show your method.

1. In the company鈥檚 prior-year survey, 80% of customers surveyed said they were 鈥渟atisfied鈥� or 鈥渧ery satisfied.鈥� Using this value as a guess for p藛, find the sample size needed for a margin of error of 3% at a 95% confidence level.

What if the company president demands 99% confidence instead? Determine how this would affect your answer to Question 1.

33. Going to the prom Tonya wants to estimate what proportion of her school鈥檚 seniors plan to attend the prom. She interviews an $SRS$ of $50$ of the $750$ seniors in her school and finds that $36$ plan to go to the prom.
(a) Identify the population and parameter of interest.
(b) Check conditions for constructing a confidence interval for the parameter.

(c) Construct a 90% confidence interval for p. Show your method.
(d) Interpret the interval in context.

34. Reporting cheating What proportion of students are willing to report cheating by other students? A student project put this question to an SRS of $172$undergraduates at a large university: 鈥淵ou witness two students cheating on a quiz. Do you go to the professor?鈥� Only$19$ answered 鈥淵es.鈥�
(a) Identify the population and parameter of interest.
(b) Check conditions for constructing a confidence interval for the parameter.
(c) Construct a $99\%$confidence interval for$p$. Show your method.
(d) Interpret the interval in context.