(b) we often read that iq scores for large populations are centered at 100. what percent of these 78 students have scores above 100? (round your answer to one decimal place.)

As IQ scores for extensive populaces are focused at 100, the mean = 100. 
There ought to be around half scores above or underneath the mean score since mean and middle is about a similar when the populace is substantial. 
P(x > 100) = P( z> (100 - 100)/sd ) = P(z > 0)= 0.5 
The number of the student who has scored over 100 = 0.5 x 78 = 39 Therefore the answer is 39 students.