standard deviation of means

Question

The mean of the scores obtained by a class of students on a physics test is 42. The standard deviation is 8%. Students have to score at least 50 to pass the test.
Assuming that the data is normally distributed,
% of the students passed the test.

Answer 1

17% pass

(100-68)/2 = 34/2= 17%

using the empirical rule 68-95-99.7 for 1-2-3 sds

68% are within 1 standard deviation of the mean

for more accurate % use z tables