Prob/Stats Unit 6 Quiz Corrections Assignment

Find the margin of error for the mean number of telephone calls directed by a local telephone company if s = 4.5 minutes, n = 420, and we want to be 95% confident.

• 0.020

• 0.432

• 0.009

• 0.117

A sample of 31 people were randomly selected from among the workers in a shoe factory. The time taken for each person to polish a finished shoe was measured, and the sample mean was 2.2 minutes with a sample standard deviation of 0.72 minutes. Construct the 90% confidence interval for the mean time to polish a shoe.

• (1.98, 2.42)

• (1.87, 2.53)

• (1.95, 2.45)

• (1.90, 2.50)

Scores on a certain test are normally distributed with a VARIANCE of 56. A researcher wishes to estimate the mean scores achieved by all adults on the test. Find the sample size needed to assure with 98% confidence that the sample mean will not differ from the population mean by more than 3 points.

• 34

• 1892

• 102

• 14

A group of 59 randomly selected students have a mean score of 38.8 with a standard deviation of 5.8 on a placement test. What is the 90% confidence interval for the mean score of all students taking the test?

• (37.0, 40.6)

• (37.3, 40.3)

• (36.9, 40.7)

• (37.5, 40.1)

For a sample with 66 observations, the mean is 33 and the standard deviation is 8.5. Use a 95% confidence level to find the margin of error for mean.

• 1.86

• 1.76

• 2.09

• 4.25

In a sample of 170 observations, there were 75 people who liked pizza. Find the margin of error for the proportion of people who like pizza given a 95% confidence level.

• 0.1310

• 0.0746

• 0.0028

• 0.0671

A survey of 300 union workers in New York State reveals that 112 favor the Independent candidate for governor. Construct the 98% confidence interval for the true proportion of all New York State union workers who favor the Independent candidate.

• (0.344, 0.402)

• (0.301, 0.0445)

• (0.316, 0.430)

• (0.308, 0.438)

Find a 95% confidence interval for proportion if n=61, x=23.

• (0.275, 0.479)

• (0.254, 0.500)

• (0.255, 0.499)

• (0.274, 0.480)

Of 92 randomly selected adults, 73.9% have health insurance. Find a 90% confidence interval for the true proportion of all adults in the town who have health insurance.

• 0.632 < p < 0.846

• 0.664 < p < 0.814

• 0.644 < p < 0.442

• 0.621 < p < 0.857

A survey of shoppers is planned to see what percentage use credit cards. Prior surveys suggest 86% of shoppers use credit cards. How many shoppers should be surveyed for a 95% confidence level if we want to be within 2% of the true population proportion?

• 1157

• 1156

• 814

• 815