...   of   a   sample   of   size   30   with   an   average   of   79.50   or   lower = NORMDIST ( 79.50 ,   99.67 ,   4.43 ,   1 ) = 2.64 E- 06. There is a very low probability that such a sample could have been observed if process performance was unchanged. We can thus...

... points for the students. The first point is that there is a reasonably high likelihood of observing the ten-day performances observed in September (both worse than before and better than before) even if the underlying process performance has not changed. The second point is that if the underlying process...