Probability using Normal distribution: Z score.

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

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

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

c. estimation the percent that did not have any dental expense.

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