Standard Deviation

Question

Suppose that the scores on particular FDMAT 108 unit exam at BYU-Idaho were approximately normally distributed with a mean of 74 and a standard deviation of 8.

 

7. About what percentage of the scores were above 90 for this unit exam?
(Round to the nearest whole number.)

8. Suppose that a cutoff score at 2 standard deviations below the mean or higher may constitute a passing grade, what was the cutoff score for a passing grade on this unit exam?

9. What is the standard score for a unit exam score of 69?
(Round to two decimals.)

Answer 1

Calculate z = ( 90 - 74 ) / 8 = 2.o

 

Look in standard normal table to see the area to the right of z = 2.0  Find it's .028 and that is your answer

 

-2 = ( x - 74 ) / 8 or

 

x-74  = -16

 

x = 58 is the score

 

Standard score = z = (69 - 74 ) / 8  = -5/8  = -.625