posted by Alexa .
Suppose. Population of test-scores 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!
I am reading your question as 65 with a standard deviation of 13. This is a population, we will use z-scores and the normal table.
(60 -65)/13 = z-score
You can then use the z-table(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 z-scores:
(65-65)/13 = 0 that will be right in the middle of the normal table.
(70-65)/13 = z.
using the table, you have to find the area between 65 and 70.
Since there are different versions of z-tables (depending on the textbook), I can't give you further directions regarding reading your z-table.