statistics
posted by general .
A countrywide estate agency specializes in selling commercial ventures. Their records show that the mean selling time is less than 90 days. Because of recent economic conditions, they believe that the mean selling time is now greater than 90 days. A countrywide survey of 100 businesses sold recently revealed that the mean selling time was 94 days, with a standard deviation of 22 days. At the 0.10 lavel of significance, has there been an increase in selling time?

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. 
z= 9094/22/√100

Determine and interpret Pearsonâ€™s correlation coefficient.