Question 1043314
The z-value for the 90th percentile is 1.28
z=(x-mu)/sd)
1.28=(x-mu)/sd
12.8=x-mu, since sd is 10 and we multiply both sides by 10.
x=mu+12.8=82.8
It is the opposite for the bottom 10%, where the z=-1.28
x-mu=-12.8
x-mu-12.8=57.2
The minimum mark to get an A is 92.8 if tenths are allowed.
The minimum mark to pass is 57.2