Shaver Manufacturing, Inc., provides dental insurance to its employees. A current study by human resource director shows the annual cost per employee for each year followed the normal probability distribution, with the mean of $1,280 and the standard deviation of $420 per year.

a. What fraction of employees cost more than $1,500 per year for the dental expenses?

b. Find out the fraction of employees cost between $1,500 and $2,000 per year?

c. Estimate percent that didn't have any dental expense.

d. What was cost for 10 percent of employees who incurred highest dental expense?