Confidence Intervals Mean Use Z or T?

A sample of 20 cupcakes found the interval for average calories to be (150, 350). Sample mean & standard deviation was known. Assume the population was normally distributed. What distribution was used?

• z

• t

• p

• neither

A quality control specialist at a glass factory must estimate the mean clarity rating for a new batch of glass using a sample of 18 glass sheets from the batch. They found the sample mean & standard deviation. Past investigations show that clarity ratings are normally distributed. choose a distribution

• neither

• p

• z

• t

Thirty randomly selected students took the calculus final. If the sample mean was 92 and the standard deviation was 9.4, construct a 99 percent confidence interval for the mean score of all students from which the sample was gathered.

• 89.08 < μ < 94.92

• 87.58 < μ < 96.42

• 87.29 < μ < 96.71

• 87.77 < μ < 96.23

In a crash test of 15 troopers, collision repair costs are found to have a distribution that is approximately normal, with a mean of $1800 and a standard deviation of $950. Construct a 99% confidence interval for the repair cost for the population.

• (1070, 2530)

• (1273, 2326)

• (1799, 1801)

• (1776, 1823)

An IQ test was given to a simple random sample of 75 students at a certain college. The sample mean score was 105.2. Scores on this test are known to have a standard deviation of 10. It is desired to construct a 90% confidence interval for the mean IQ scores of the students at the college.

• (104.6,108.9)

• (103.4,107.2)

• (103.3,107.1)

• (104.3,108.2)

The lifetime of a certain type of batter is known to be normally distributed with a standard deviation of 20 hours. A sample of 50 batteries had a mean lifetime of 120.1 hours. It is desired to construct a 99% confidence interval for the mean lifetime of this type of battery.

What is the Confidence Interval to one decimal place?

• (114.5, 125.6)

• (112.8, 127.4)

• (112.82, 127.38)

• (114.56, 125.64)

A research group wishes to estimate the mean amount of time (in hours) that members of a fitness center spend exercising each week. They want to estimate the mean within a margin of error of 0.5 hours with a 95% level of confidence. Previous data suggests that the standard deviation of the population is 2.2. Which of the following is the smallest sample size they could use? (use n formula)

• 60

• 75

• 90

• 180

The football coach randomly selected ten players and timed how long each player took to perform a certain drill. The times (in minutes) were: 13.2, 5.1, 7.5, 8.0, 12.7, 7.6, 13.8, 14.5, 7.7, and 10.5. Determine a 95 percent confidence interval for the mean time for all players. Assume times are normally distributed.

• 12.30 < μ < 7.82

• 7.82 < μ < 12.30

• 7.7 < μ < 12.40

• 12.40 < μ < 7.72

A sample of 29 people owned an average of 1.35 apple products. It is known from a previous study that the population standard deviation of apple product ownership is 0.63 products. Construct a 95% confidence interval. Assume the population is normally distributed. Choose a distribution.

• t

• z

• neither

• p

A random sample of 19 students has a grade point average with a mean of 2.86 and the standard deviation is 0.78. Assume the population is normally distributed. Choose a distribution.

• neither

• z

• p

• t