On a nationwide math test, the mean was 75 and the standard deviation was 10. If Roberto scored 70, what was his z-score?

Answer 1

First we assume a normal distribution of the scores (given the nationwide sample and need to estimate the z score). In this case, the standardized z-score is calculated as z= (x-μ)/σ, where μ is the mean and σ is standard deviation. Therefore z=(70-75)/10 = -0.5.