In October 2005 the average Australian credit-card account balance was $2,604, according to data extracted from the Reserve Bank of Australia. Assuming that these balances are approximately normal with a mean of $2,604 and a standard deviation of $1,500:

(a) Find the probability that an account balance is less than $2,500.

(b) Find the probability that an account balance is more than $5,000.

(c) What proportion of account balances are between $3,000 and $4,000?

(d) 99% of account balances are less than what amount?