Question

The grades on the last math exam had a mean of 88%. Assume the population of grades on math exams is known to be normally distributed with a standard deviation of 6. What percent of students earn a score between 72% and 90%?

Answer 1

you need to find the value of z for both the values given as 72 and 90 against mean 88
and then add them and finally express it as %
using
z= (x-88)/6 ...

Answer 2

Yes and n, find z=(value-mean)/sd for 90 and for 72 as values,
then use tables to get the percentages between these z values, rather than
the sum of these .