Statistics Question standard score T score

Question

I need to know the answer to the following question and if possible how the answer was found:

 

If I obtain a score of 100 on a test that has a mean of 120 and a standard
deviation of 10, what is my standard score? What would be my T score (mean
of 50 and standard deviation of 10)?

Answer 1

z= (100-120)/10 = -20/10 =-2

by the empirical rule you are near the bottom of the heap, a 2.5 percentile, with 97.5% of the class with higher grades. You did beat 2.5% of the students though. If a class of 500, you beat .025 x 500 = 12 1/2 students