Question

The time required to finish a test in normally distributed with a mean of 80 minutes and a standard deviation of 15 minutes. What is the probability that a student chosen at random will finish the test in more than 95 minutes?

Answer 1

The z-score for 95 minutes is:
$z=\frac{X-\mu}{\sigma}=\frac{95-80}{15}=1$
Reference to a standard normal distribution shows that the required probability is approximately 0.16 or 16%.