Records of 40 used passenger cars and 40used pickup trucks were randomly sampled to investigate
          whetherthere was any significant difference in the mean time in years thatthey were kept by the original
          ownerbefore being sold.  For the sampled cars, the mean was5.3 years with a standard deviation of 2.2
          years.  Forthe sampled pickup trucks, the mean was 7.1 years with a standarddeviation of 3.0 years. Â
          (Assumethat the two samples are independent.)
a)Â Â Construct and interpret the 90% confidenceinterval estimate of the difference between the mean time for allpassenger cars and the mean time for all pickup trucks.
b)  Does there appear to be a significant differencebetween the two population means?  Is one higher than
               theother?  If so, who keeps their vehicles longer?
