According to the Internal Revenue Service, the mean tax refund for the year 2013 was $3,000. Assume the standard deviation is $450 and that the amounts refunded follow a normal probability distribution.
a. What percent of the refunds are more than $3,100?
b. What percent of the refunds are more than $3,100 but less than $3,500?
c. What percent of the refunds are more than $2,250 but less than $3,500?