According to the Federal Reserve Board, the average credit card debt per U.S. household was $8,565 in 2008. Assume that the distribution of credit card debt per household has a normal distribution with a standard deviation of $3,000.

a. Determine the percentage of households that have a credit card debt of more than $13,000.

b. One household has a credit card debt that is at the 95th percentile. Determine its credit card debt.

c. If four households were selected at random, determine the probability that at least half of them would have credit card debt of more than $13,000.