Wells Fargo has realized that they lose home mortgage business to other banks that can process the loan applications with less variability in the time it takes to process each application. The bank recently studied this problem, and found that the processing time T is normally distributed with a mean of 13 days. They didnt measure the standard deviation, but they know that 50% of all applications were processed in between 10.5 and 15.5 days. After learning all this, they then fired half of their mortgage loan officers and replaced them with new recruits. They then sampled 25 applications, and found a sample mean of 13 days (same as the old) and a sample standard deviation of 2.5 days. (a) Test whether their actions have significantly changed their processing time T.
(b) Based on the sample of 25 applications, give a 90% confidence interval for the parameter that
has changed.