Statistics Confidence Interval

The heights of 5-year old boys are approximately normal. The mean height of a random sample of 37 5-year old boys is found to be 30 inches with a standard deviation of 3 inches. What is the standard error of x̄?

• .493

• 1.32

• 5.77

• 1.96

Find the critical value z_c necessary to form a 98% confidence interval.

• 2.33

• 2.05

• 0.5040

• 0.8365

A random sample of 42 textbooks has a mean price of $114.50 and a standard deviation of $12.30.

Find a 98% confidence interval for the mean price of all textbooks.

• (111.38, 117.62)

• (110.08, 118.92)

• (110.78, 118.22)

• (109.61, 119.39)

Determine the minimum sample size needed to construct a 95% confidence interval for the mean age of employees at a company. The estimate must be accurate to within 0.5 year. Assume the standard deviation is 4.8 years.

• 18

• 19

• 354

• 355

A random sample of 15 DVD players has a mean price of $64.30 and a standard deviation of $5.60.

Find a 95% confidence interval for the mean price of all DVD players.

• (61.20, 67.40)

• (61.47, 67.13)

• (61.22, 67.38)

• (61.10, 67.51)

In a survey of 250 Internet users, 195 have high-speed Internet access at home.

Find a 90% confidence interval for the proportion of all Internet users who have high-speed Internet access at home.

• (1.19, 1.38)

• (0.728, 0.832)

• (0.731, 0.829)

• (0.737, 0.823)

You want to estimate, with 95% confidence, the proportion of households with pets. Your estimate must be accurate within 3% of the population proportion. No preliminary estimate is available. Find the minimum sample size needed.

• 1141

• 3267

• 1068

• 1067

A random sample of 42 textbooks has a mean price of $114.50 and a standard deviation of $12.30.

Find a point estimate for the mean price of all textbooks.

• $42

• $12.30

• $114.50

• $2.73

Find the critical value t_c necessary to form a 95% confidence interval with a sample size of 15.

• 1.960

• 2.145

• 2.131

• 2.120

In a survey of 250 Internet users, 195 have high-speed Internet access at home.

Find a point estimate for the proportion of all Internet users who have high-speed Internet access at home.

• 28

• 0.78

• 0.22

• 195