A random sample of 13 students were asked how long it took them to complete a...
A random sample of 13 students were asked how long it took them
to complete a certain exam. The mean length of time was 105.5
minutes, with a standard deviation of 66.7 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.
Homework Answers
Solution :
Given that,
t
,df = 1.356
Margin of error = E = t,df
* (s /
n)
= 1.356 * (66.7 /
13)
Margin of error = E = 25.1
The 90% lower confidence interval estimate of the population mean is,
- E
105.5 - 25.1
80.4
lower bound : 80.4
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