Exercise 4. Old Faithful: The most famous geyser in the world, Old Faithful in Yellowstone National Park, has a mean time between eruptions of 85 minutes. If the interval of time between eruptions is normally distributed with standard deviation 21.25 minutes, answer the following questions: Source: www.unmuseum.org

(4a) (10pts) What is the probability that a random sample of 20 time intervals between eruptions has a mean longer than 95 minutes? Draw a picture

(4b) (10pts) What is the probability that a random sample of 30 time intervals between eruptions has a mean longer than 95 minutes? Draw a picture