Question

Test scores on a university admissions test are normally distributed, with a mean of 500 and a standard deviation of 100.
a. What is the probability that a randomly selected applicant scores between 425 and 575?
b. What is the probability that a randomly selected applicant scores 625 or more?
  c. What is the probability that a randomly selected applicant scores less than 500?
d. Twenty per cent of test scores exceed what value?

Answer 1

plug in your numbers and play around with Z table stuff at

http://davidmlane.com/hyperstat/z_table.html

Answer 2

OR… just in case your computer crashes, you could use this equation:

Z = (score-mean)/SD

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions/probabilities related to the Z scores.

For d, just reverse the process. Find .20, insert its Z score and find the raw score.