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Measurement of the waiting time of 45 randomly selected patients at a hospital emergency room gave mean and sample standard deviation 11.3 and 6.5 minutes, respectively. A 90% confidence interval for the mean waiting time of all patients is about

(11.3-2.05*6.5/√45, 11.3+2.05*6.5/√45)

(11.3-1.96*6.5/√45, 11.3+1.96*6.5/√45)

(11.3-1.680*6.5/√45, 11.3+1.680*6.5/√45)

(11.3-1.645*6.5/√45, 11.3+1.645*6.5/√45)

(11.3-1.679*6.5/√45, 11.3+1.679*6.5/√45)

2.A random sample of 500 observations yields X¯

=400 and S=50. Which of the following is the correct 95% confidence interval for the population mean μ (round up to two decimal places).

(395.62, 404.38)

(397.14, 402.86)

(261.41, 538.59)

(283.68, 516.32)

(396.32, 403.68)

3.Suppose an insurance company wants to determine the average speed of cars passing through an intersection. They randomly selected 85 cars and found their average speed to be 42 miles per hour with standard deviation of 4.2 miles per hour. A 90% confidence interval for the average speed of all the cars passing through the intersection is

(38.12, 45.12)

(42.53, 43.67)

(39.52, 44.72)

(41.25, 42.75)

(40.09, 43.91)

4.A 95% confidence interval for a population mean is constructed from a sample of size 40. Which of the following statements are true?

I. The population mean must lie in the interval constructed from the data.

II. A 90% confidence interval constructed from the same data will be narrower.

III. If the sample mean and standard deviation had the same values, but came from a sample of size 400, the interval constructed would be narrower.

I, II, and III

Only I

Only III

Only I and III

Only II and III

5.Given that the population standard deviation is σ=5.6, determine the minimum sample size needed in order to estimate the population mean so that the margin of error is E=0.5 at the 90% level of confidence.

n=340

n=106

n=207

n=265

n=19