American Express charges merchants higher fees than any other credit or debit card, according to the USA Today article “American Express fees take flak” (December 23, 2004). The company believes they can do this because they claim the customers using the American Express card spend more. The average annual charges per card in 2003 were $9600 according to data from American Express and The Neilson Report. Assuming that the annual charges per card are approximately normally distributed with a standard deviation of $2100, what is the probability that an American Express customer’s annual charges are:

a. Less than $4000

b. Between $5000 and $10,000

c. Greater than $16,000