A large metropolitan area found that the time it takes for people to commute to work has a mean of 20.5 minutes and a standard deviation of 15.4 minutes. What is the probability that a random sample of 40 people have a mean commute time greater than 25 minutes?

Answer 1

z-score = (25-20.5)/15.4

then look up that z in your tables,
subtract that from 1
that is,
1 - value you looked up

or

you can use one of my favourite websites

http://davidmlane.com/normal.html

Make sure "area from value " is clicked on
enter the mean, the sd, and click on "below" and enter 25
The value of .6149 should agree with the value you found above