Toby’s Trucking Company determined that the distance traveled per truck per year is normally distributed, with a mean of 50 thousand miles and a standard deviation of 12 thousand miles.

a. What proportion of trucks can be expected to travel between 34 and 50 thousand miles in a year?

b. What percentage of trucks can be expected to travel either less than 30 or more than 60 thousand miles in a year?

c. How many miles will be traveled by at least 80 percent of the trucks?

d. What are your answers to (a) through (c) if the standard deviation is 10 thousand miles?