Question 1167595
z=(x-mean)/sd
a. z is >-2 and that has probability 0.9772
b. z<-3.6 and that probability is 0.00016
c. x< 75 and x>90 is z<-2.5 and z >-1
that probability is 0.0062 and 0.8413 or sum 0.8475

90% of the values are between z=-1.645 and +1.645 or between 83.55 and 116.45