Apopulation has a mean of 50 and a standard deviation of 4. how many standard deviations above the mean is a data value of 60?

a. 2.5
b. 2
c. 1.5
d. 3

One way of approaching the solution of this problem is to use the "z-score" formula.  The z-score tells us how many s. d. a given point is above or below the given mean.

The formula for z score is as follows:

        x-mean
z =
           s. d.

Thus, with mean =50 and std. dev. = 4, we get 

        x-mean                    60-50
z =        z = = 10/4 = 2.5
           s. d.                          4
   
         Thus, 60 is 2.5 std. dev. above the mean, 50.