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.

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

2. What percentage of trucks can be expected to travel either below 30 or above 60 thousand miles in a year?

3. How many miles will be traveled by at least 80% of the trucks?

4. What are your answers to (1) through (3) if the standard deviation is 10 thousand miles?