6.67 Used car prices Data from the Web site carmax.com compiled in July 2014 show that prices for used Audi A4 cars advertised on the Web site have a mean of $23,800 and a standard deviation of $4,380. Assume a normal distribution for the price.

a. What percent of used Audi A4s cost more than

$25,000?

b. What percent of used Audi A4s cost between $18,000 and $22,000?

c. The least expensive 10% of used Audi A4s offered on the Web site cost at most how much?