A machine produces metal rods used in an automobile suspension system. A random sample of 15 rods is selected and the diameter is measured. The resulting data (in millimeters) are as follows: No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Dia. 8.21 8.21 8.23 8.25 8.26 8.23 8.20 8.26 8.19 8.23 8.20 8.28 8.24 8.25 8.24

Use the data above to calculate a 95% two-sided confidence interval on the mean rod diameter. Assume the data are normally distributed.

a. Calculate the sample mean and standard deviation.
b. Calculate the 95% two-sided confidence interval on the true mean rod diameter.

a. the sample mean is 8.232  and standard deviation is 0.025967012040004

You can be 95% confident that the difference between your two population means (μ1 - μ2) lies between -0.01942 and 0.01942.

Step-by-step explanation:

correct answer is c. just did it

step-by-step explanation:

yes, gavin is right.

step-by-step explanation:

gavin is correct. 

this problem is about converting 9% per year to how many percent per quarter. the rate is still the same. it only differed in the time period. so, through dimensional analysis,

9% per year  × (1 year / 4 quarters) = 2.25% per quarter

if he was asked to convert 9% per year to how many percent per quarter  compounded quarterly, then you will not simply divide by four. this is because compounding is not linear.

hope this , have a good day. c;