an automobile manufacturer claims that their van has a 28.228.2 miles/gallon (mpg) rating. an independent testing firm has been contracted to test the mpg for this van. after testing 2727 vans they found a mean mpg of 28.028.0 with a standard deviation of 2.62.6. is there sufficient evidence at the 0.010.01 level that the vans underperform the manufacturer's mpg rating? assume the population distribution is approximately normal.