confidence intervals 6.1-6.2

Find the critical value Zc that corresponds to a 98% confidence level

• 2.33

• 1.645

• 1.96

• 2.575

Determine the sampling error if the grade point averages for 10 randomly selected students from a class of 125

students has a mean of x = 2.3. Assume the grade point average of the 125 students has a mean of μ = 2.7.

• 0.04

• 2.5

• -0.4

• 2.1

Find the margin of error for the given values of c, σ, and n.

c = 0.90, σ = 10.2, n = 75

• 1.06

• 1.94

• 0.22

• 1.18

In a recent study of 42 eighth graders, the mean number of hours per week that they watched television was

19.6. Assume the population standard deviation is 5.8 hours. Find the 98% confidence interval for the

population mean.

• (14.1, 23.2)

• (18.3, 20.9)

• (17.5, 21.7)

• (19.1, 20.4)

In a sample of 10 randomly selected women, it was found that their mean height was 63.4 inches. From

previous studies, it is assumed that the standard deviation σ is 2.4 and that the population of height

measurements is normally distributed. Construct the 95% confidence interval for the population mean.

• (61.9, 64.9)

• (58.1, 67.3)

• (59.7, 66.5)

• (60.8, 65.4)

The standard IQ test has a mean of 97 and a standard deviation of 17. We want to be 95% certain that we are

within 5 IQ points of the true mean. Determine the required sample size.

• 45

• 154

• 72

• 10

A nurse at a local hospital is interested in estimating the birth weight of infants. How large a sample must she

select if she desires to be 99% confident that the true mean is within 4 ounces of the sample mean? The

standard deviation of the birth weights is known to be 9 ounces.

• 30

• 7

• 15

• 34

Find the critical value, tc for c = 0.99 and n = 10.

• 3.169

• 3.250

• 2.262

• 1.254

Find the value of E, the margin of error, for c = 0.90, n = 16 and s = 2.4.

• 0.26

• 0.08

• 2.54

• 1.05

Construct a 95% confidence interval for the population mean, μ. Assume the population has a normal

distribution. A sample of 20 college students had mean annual earnings of $3120 with a standard deviation of

$677.

• ($1324, $1567)

• ($2135, $2567)

• ($2803, $3437)

• ($2657, $2891)