Scores on a test are normally distributed with a mean of 68.9 and a standard deviation of 11.6. Find P81, which separates the bottom 81% from the top 19%.
A) 79.1
B) 72.3
C) 0.291
D) 0.88

Question

Quizplus · Accepted Answer

P81 corresponds to the 81st percentile of a normal distribution. Using the z-score table, the z-score for 0.81 is approximately 0.88. Using the formula X = μ + zσ, where μ is the mean and σ is the standard deviation, we calculate X = 68.9 + 0.88(11.6) = 79.1.

Scores on a Test Are Normally Distributed with a Mean