In 2018, a population of 1,500,000 students took the GMAT test. The distribution of scores in the math section of the test follows a normal distribution with mean µ = 600 and standard deviation σ = 120.
a) Calculate the Z-score for a test score of 480. Interpret it using a complete sentence.
b) The GRE math test is an alternate to the GMAT. The test score for the student who did GRE instead of GMAT is also normally distributed with mean µ = 20 and standard deviation σ = 6. If the score of one student who has done both GMAT and GRE test is respectively 650, and 22, in which test he has performed better?