According to J.D. Power&Associates, the mean purchase price of a smartphone device (such as an iphone or Blackberry) in 2008 was$216. In 2009, a random sample of 20 business managers who owned a smartpbone device showed a mean purchase price of $209 with a sample standard deviation of $13. (a) At a= .05, has the mean purchase price decreased? State the hypotheses and decision rule clearly. (b) Use Excel to find the p-value and interpret it