Imagine the average score on this exam ends up being 71 with a standard deviation of 10. If scores are normally distributed, ______ is the lowest score that would place you in the top 20% of the class.
A) 71
B) 76
C) 80
D) 84

Question

Quizplus · Accepted Answer

To find the lowest score that would place you in the top 20% of the class, we need to find the score that corresponds to the 80th percentile. Using a standard normal distribution table, we can find that the z-score that corresponds to the 80th percentile is approximately 0.845.

We can use the formula z = (x - μ) / σ to solve for x, where x is the score we are trying to find, μ is the mean of 71, σ is the standard deviation of 10, and z is the value we found from the table.

0.845 = (x - 71) / 10
8.45 = x - 71
x = 80.45

Therefore, the lowest score that would place you in the top 20% of the class is 80. Answer choice C is the correct one.

Imagine the Average Score on This Exam Ends Up Being