Posted by carole on .
tire co. has produced 614 tires a day. (standard dev. of 36). they changed process to see if it increases amount of tires made. The sample mean is 620. alpha is .05 and n=16

stats 
PsyDAG,
If you are testing for significant differences:
Z = (mean1  mean2)/standard error (SE) of difference between means
SEdiff = √(SEmean1^2 + SEmean2^2)
SEm = SD/√n
If only one SD is provided, you can use just that to determine SEdiff.
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.