What is students’ A and B z-score? if $mean=81$, $SD=4$, distribution is normally distributed.
(student A scored $72$, and student B scored $86$).
what is the $z-score$ value for both student A and student B
student A $z-score(72) = (72 - mean)/SD = (72 - 81)/4 = - 2.25$
student B $z-score(86) = (86 - mean)/SD = (86 - 81)/4 = - 1.25$
now the question is what is the $z-score$ value for both student A and student B, is it:
1- student A $z-score$ + student B $z-score$ = $- 2.25 + - 1.25 = - 3.5$
or
2- student A and student B $z-score(72+86)$ = $z-score(153) = (153 - mean)/SD = (153 - 81)/4 = 18$
Or when it comes to calculate more than 0ne $z-score$ together, we should use another way? Thanks