If 500 students took the exam, approximately how many students scored below 75

67 + 8 z = 75

z = 1

Looking at a z-score chart (see http://easycalculation.com/statistics/positive-z-score-chart.php) we find that 84.13% of the population is below z = 1.

So 84.13% * 500 = 84.13 * 5 = 84.13 * 10 / 2 = 841.3 / 2 = 420 students scored below 75%.