According to the Internal Revenue Service, the mean tax refund for the year 2007 was $ 2,708. Assume the standard deviation is $ 650 and tha the amounts refunded follow a normal probability distribution.

a. What percent of the refunds are more than $ 3,000?

b. What percent of the refunds are more than $ 3,000 but less than $ 3,500?

c. What percent of the refunds are more than $ 2,500 but less than $ 3,500?