Question 1133149
z=(x-mean)/sd
>=(33.3-52)/16 or -18.7/16 or greater than -1.17
probability is 0.8790
or 88 students

more than 80% is >=(80-52)/16 or z>=1.75 or probability 0.0400 or 4 students

for 70%, >=(70-52)/16 or 1.125 or 0.1303.  This is 13 students minus the 4 that get A or 9 students altogether.