Independent samples of 400 observations

Independent samples of 400 observations are selected from two populations.

Sample 1 Sample 2

mean= 5275 mean= 5240

standard deviation= 150 standard deviation= 200

a) Use a 90% confidence interval to estimate (µ1-µ2)

b) Test the null hypothesis µ1-µ2= 25 against the alternative hypothesis µ1-µ2≠ 25 at the significance level a= .05