Construct a 95 percent confidence interval for the true mean

Construct a 95 percent confidence interval for the true mean order size. (Round your answers to the nearest whole number.)

Solution

Sample mean=27185.9

sample standard deviation =17071.76

The degree of freedom =n-1=10-1=9

Given a=1-0.95=0.05, t(0.025, df=9) =2.26 (from student t table)

So the lower bound is

xbar - t*s/vn=27185.9- 2.26*17071.76/sqrt(10) =14985

So the upper bound is

xbar + t*s/vn=27185.9+ 2.26*17071.76/sqrt(10) =39387