* Suppose commute times in a large city are normally distributed and that 66.60% of commuters in this city take more than 20 minutes to commute one way. If the standard deviation of such commutes is 6.4 minutes, what is the mean commute? (Round to 3 decimal places)

* Assume a normal distribution and find the following probabilities. (Round to 2 decimal) P( 15 < x <23 | =21 and =3) * According to the Air Transport Association of America, the average operating cost of an MD-80 jet airliner is $2,270 per hour. Suppose the operating costs of an MD-80 jet airliner are normally distributed with a standard deviation of $ 175 per hour. (Round the value of z to 2 decimal places)

(a) At what operating cost would only 23% of the operating costs be less? (b) At what operating cost would 65% of the operating costs be more? (c) What operating cost would be more than 85% of operating costs?