Introduction to Statistics

Question

The mean grade for Test 2 in Marquettas biology class is 73 ,and the standard deviation is 8 points. If the standard score for Marquettas test is 1.25, what is her grade?

Answer 1

A standard score is a z-score. A z-score is the distance of a single score (X) from the mean (M) in units of standard deviation (SD). The formula is as follows:

Standard Score = (X - M)/SD

In your example, we have 1.25 = (X - 73)/8.

We can multiply both sides by 8 to get 10 = X - 73

Then we can add 73 to both sides to get 83 = X. So her grade was 83.