Exam 18: Confidence Intervals for Proportions

In a poll of 2,778 voters in a certain city,77% said that they supported the Conservative Party of Canada.The margin of error in the poll was reported as 6 percentage points (with a 95% degree of confidence).Make a statement about the adequacy of the sample size for the given margin of error.

When 278 college students are randomly selected and surveyed,it is found that 110 own a car.Construct a 99% confidence interval for the percentage of all college students who own a car.

You want to estimate the average gas price in Canada for a litre of regular unleaded gasoline.You take a random sample of prices from 100 gas stations,recording an average cost of $1.37 and a standard deviation of $0.11.Create a 99% confidence interval for the mean price per litre of regular unleaded gasoline.

In a survey of 1,300 T.V.viewers,30% said they watch network news programs.Find the margin of error for this survey if we want 95% confidence in our estimate of the percent of T.V.viewers who watch network news programs.

A pollster wishes to estimate the true proportion of voters in Ottawa,Ontario who support the Conservative party.How many voters should be surveyed in order to be 95% confident that the true proportion is estimated to within 4%?

A survey of 300 students at York University revealed that 112 favour an NDP candidate for M.P..Construct a 98% confidence interval for the percentage of all York University students who favour an NDP candidate.

A study involves 673 randomly selected deaths,with 34 of them caused by accidents.Construct a 98% confidence interval for the percentage of all deaths that are caused by accidents.

In a poll of 553 voters in a certain city,64% said that they supported the NDP in an upcoming election.The margin of error in the poll was reported as 4 percentage points (with a 95% degree of confidence).Make a statement about the adequacy of the sample size for the given margin of error.

A political party is interested in finding out what kind of popular support they might expect on an environmental initiative.Similar issues have gotten 87% support.The committee will set up a polling program to assure 95% confidence that the margin of error is less than 9%.What sample size will suffice?

You want to estimate the average gas price in your city for a litre of regular unleaded gasoline.From your sample of 15 gas stations,you calculate a 95% confidence interval of ($1.34,$1.40)

Of 88 adults selected randomly from one town,60 have health insurance.Construct a 90% confidence interval for the percentage of all adults in the town who have health insurance.

A local bank needs information concerning the checking account balances of its local customers.A random sample of 144 accounts was checked and yielded a mean balance of $664.14 and a standard deviation of $297.29.Find a 98% confidence interval for the true mean checking account balance for local customers.

How much fat do reduced fat cookies typically have? You take a random sample of 120 reduced-fat cookies and test them in a lab,finding a mean fat content of 4.2 grams.You calculate a 95% confidence interval and find that the margin of error is ±0.8 grams.

A newspaper reports that 58% of farmers are planning to plant genetically modified crops this year.The article adds that the poll is based on a random sample of 798 farmers and has a margin of error of 4.5%.

A recent poll of 1500 new home buyers found that 60% hired a moving company to help them move to their new home.Find the margin of error for this poll if we want 95% confidence in our estimate of the percent of new home buyers who hired movers.

A poll of 2841 registered voters in a certain town indicated that 70% would vote for the Liberal Party of Canada.The margin of error for this poll was 2%.