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? (Round the intermediate values to 2 decimal places. Round your answer to 2 decimal places.)

b) What percent of the refunds are more than $3,100 but less than $3,500? (Round the intermediate values to 2 decimal places. Round your answer to 2 decimal places.)

c) What percent of the refunds are more than $2,250 but less than $3,500? (Round the intermediate values to 2 decimal places. Round your answer to 2 decimal places.)