A random sample of 60 employees at a company showed an avera

A random sample of 60 employees at a company showed an average work time of 9 hours and a sample standard deviation of 2 hours. Find the 90% confidence interval for the true average work time of all employees in the company. Round your answer to three decimal places

Solution

Confidence Interval
CI = x ± t a/2 * (sd/ Sqrt(n))
Where,
x = Mean
sd = Standard Deviation
a = 1 - (Confidence Level/100)
ta/2 = t-table value
CI = Confidence Interval
Mean(x)=9
Standard deviation( sd )=2
Sample Size(n)=60
Confidence Interval = [ 9 ± t a/2 ( 2/ Sqrt ( 60) ) ]
= [ 9 - 1.671 * (0.258) , 9 + 1.671 * (0.258) ]
= [ 8.569,9.431 ]