The numbers of cookies in a shipment of bags are normally distributed, with a mean of 64 and a standard deviation of 4. What percent of bags of cookies will contain between 64 and 68 cookies?

17%

68%

47.5%

34%

The z score for 60 is (60 - µ) / σ = (60 - 64) / 4 = - 1. Thus, 60 falls one standard deviation below the mean.

By the empirical rule, 68% of the observations fall between z = - 1 and z = + 1.

We have half of that (z = - 1 to z = 0), so the answer is 68/2 = 34.