Question

10) A random sample of 13 students were asked how long it took them to complete a certain exam. The mean length of time was 120.1 minutes, with a standard deviation of 84.0 minutes. Find the lower bound of the 90% confidence interval for the true mean length of time it would take for all students to complete the exam.

Round to one decimal place (for example: 108.1). Write only a number as your answer. Do not write any units.

11) For a population of people who completed their GED, the average age at completion was 31.8 and the standard deviation was 4.6. The distributions of ages was approximately bell-shaped. Compute the z-score for an individual who completed their GED at the age of 20 .

Write only a number as your answer. Round your answer to two decimal places (for example: 3.15).

Answer 1

(10). The formula to calculate the Lower bound of the 90% confidence interval for is given by

In the question we have asked to find the lower bound of the 90% confidence interval for the true mean length of time that would take for all students to complete the exam, i.e.,

Given:

Critical value: For 90% confidence,

So, the lower bound of the 90% confidence interval for the true mean length of time that would take for all students to complete the exam is calculated as 88.5

(11). Z-score when population standard deviation is known is given as -

; its the population mean age people who completed their GED

; population standard deviation

; age of an individual who completed GED at the age of 20

So, the Z-score for an individual who completed GED at the age of 20 is calculated as -2.57