Respuesta :
Answer:
The 95% confidence interval on the mean cycle time for this machine is between 8.98 minutes and 11.44 minutes.
Step-by-step explanation:
We are in posession of the sample's standard deviation, so we use the students' t-distribution to solve this question.
The first step to solve this problem is finding how many degrees of freedom, we have. This is the sample size subtracted by 1. So
df = 21 - 1 = 20
95% confidence interval
Now, we have to find a value of T, which is found looking at the t table, with 20 degrees of freedom(y-axis) and a confidence level of [tex]1 - \frac{1 - 0.95}{2} = 0.975([tex]t_{975}[/tex]). So we have T = 2.086
The margin of error is:
M = T*s = 2.086*0.59 = 2.13
In which s is the standard deviation of the sample.
The lower end of the interval is the sample mean subtracted by M. So it is 10.21 - 1.23 = 8.98 minutes
The upper end of the interval is the sample mean added to M. So it is 10.21 + 1.23 = 11.44 minutes
The 95% confidence interval on the mean cycle time for this machine is between 8.98 minutes and 11.44 minutes.