In a research sample of high school students, the variable "number of MySpace friends" formed a normal distribution with a mean of 45 and a standard deviation of 16. Valentina had 53 friends. What was her approximate percentile rank?
A) 31st
B) 53rd
C) 69th
D) 49th

Question

Quizplus · Accepted Answer

We need to find the percentile rank of Valentina, who has 53 friends.

First, we need to standardize her score by finding the z-score:

z = (x - mean)/standard deviation
z = (53 - 45)/16
z = 0.50

Using a standard normal table, we can find that the area to the left of z = 0.50 is approximately 0.6915 or 69.15%.

Therefore, Valentina's approximate percentile rank is 69th.

In a Research Sample of High School Students, the Variable