Answer question no 30 given below:
solution:-
The nearest that I can see to 90% =0.9 on the normal tables is 0.5+0.3997
z for 0.3997 =1.28
z= [x-u]/s > /= 1.28
z=[ x-72]/9 > 1.28
x >[ 1.28]9 +72 =83.52 marks
That is , a grade must be greater than 83.52 marks in order to fall into the top 10%