Question

The time required to finish a test in normally distributed with a mean of 70 minutes and a standard deviation of 10 minutes. What is the probability that a student chosen at random will finish the test in less than 60 minutes?

Answer 1

Note that 60 minutes is 1 standard deviation away from the mean and from recalling the 68-95-99.7 rule, the area that will remain is (100 - 68) = 32%. However, we only want the leftmost portion of this area, so the answer is 32%/2 = 16%. 

Choose D.