One Population Mean Confidence Interval Sigma

What is the correct z_a/2 to use for 95% confidence?

• 2.58

• 1.96

• 1.65

• 2.08

If you would like to be 95% confident, what is the value of alpha?

• 95%

• 5%

• 2.5%

• 1%

• 5.01, 6.39

• 5.11, 6.39

• 5.31, 6.39

• 5.21, 6.39

Suppose that you find a 98% confidence interval for the life span, in months, of a certain brand of light bulb is ( 23.5, 25.7). Which of these is a valid interpretation of this confidence interval?

• There is a 98% probability that the true average life span of one of these light bulbs is between 23.5 and 25.7 months.

• There is a 98% probability that a randomly selected light bulb lasted between 23.5 and 25.7 months.

• We are 98% confident that the average life span of one of these light bulbs in our sample between is 23.5 and 25.7 months.

• We are 98% confident that the true average life span of this light bulbs is between 23.5 and 25.7 months.

In a sample size of 100, the mean is 75 and the standard deviation is 3.5. What is the margin of error, to the nearest hundredth, for a confidence interval of 95%? Formula: E = Z_c (σ/√n)

• 0.960

• 0.761

• 0.314

• 0.686

Using the Z-table, find the Z critical value that is associated with 98% confidence level?

• 2.576

• 1.960

• 1.282

• 2.326

A college is concerned about the impact of students working while they are enrolled in classes and the effect it has on their performance. In order to do any research, they must first estimate the amount of time that students spend working. They know from previous studies that the population standard deviation of this variable is about 2.75 hours. A survey of 50 students provides a sample mean of 5.75 hours worked.

Identify the population and sample.

• Population: All college students.

  Sample: All students randomly selected.

• Population: All students at a college.

  Sample: 50 students randomly selected.

• Population: All college students in the USA.

  Sample: The 50 students who are selected.

A college is concerned about the impact of students working while they are enrolled in classes and the effect it has on their performance. In order to do any research, they must first estimate the amount of time that students spend working. They know from previous studies that the population standard deviation of this variable is about 2.75 hours. A survey of 50 students provides a sample mean of 5.75 hours worked. What critical value is the most appropriate to use and why?

• z-value because n greater than 30

• t-value because n is greater than 30

• z-value since n is less than 30

• t-value since n is less than 30

An observational study found that 123 out of 500 shoppers who entered a local grocery store purchased eggs during their visit. Suppose were to use this information to create a confidence interval for this local grocery store shoppers who buy eggs when they come into the store. What is the appropriate critical value for 98% confidence interval would be?

• 1.282

• 2.576

• 1.960

• 2.326

• 0.045

• 0.076

• 0.025

• 0.047