Question 530:

Asked on December 2, 2008

Tags: Z-Score , Percent Score

1

Answer:

No answer provided yet.

First thing we need to do is find the z-score corresponding to 90 percent of the area under the normal curve. Since we want to know the percentile score, we're interested in the 1-sided area. We can use a z-table in the back of a statistics text or the percentile to z-score calculator , select 1-sided and we get 1.2817.

Now we setup a simple equation to solve for the unknown score that provides us with this z-score. Recall that a z-score is calculated by subtracting the mean from the score and dividing that result by the standard deviation.

1. (x-40)/7 = 1.2817
2. x-40 = 8.9719
3. x = 48.9719

So a score of 48.97 would have gotten in the 90th percentile, meaning scoring higher than 90 percent of other scores.