Posted by Alexa on Sunday, March 10, 2013 at 3:38pm.
Suppose. Population of testscores is normally distributed with mean 65 and standard deviation 13 x~n (65,13) if you select a test at randome what is the probability that the score is below 60 or that it is between 65 and 70 please show work!

Statistics  Dr. Jane, Sunday, March 10, 2013 at 6:40pm
I am reading your question as 65 with a standard deviation of 13. This is a population, we will use zscores and the normal table.
Below 60
(60 65)/13 = zscore
You can then use the ztable(normal table) to find the area under the lower tail and this will give you the probability of a score under 60
Between 65 and 70
You have to find both zscores:
(6565)/13 = 0 that will be right in the middle of the normal table.
(7065)/13 = z.
using the table, you have to find the area between 65 and 70.
Since there are different versions of ztables (depending on the textbook), I can't give you further directions regarding reading your ztable.