The scores on a first test are unimodal and symmetric with mean 75 points and standard deviation 8 points.
a. Find the approximate percentage of scores within three standard deviations of the mean.
b. Find the approximate percentage of scores between 67 points and 83 points.
c. If 40 students took the test, then find the number of students who scored between 59 points and 91 points.
d. On the second test, the mean is 70 points and the standard deviation is 10 points. Compare the center of the first-test scores and the center of the second-test scores. Also, compare the spread of the first-test scores and the spread of the second-test scores.