smilar question from NET D- 8707

The aging algorithm with a = 1/2 is being used to predict run times. The
       previous for runs, from oldest to most recent, are 40, 20, 40, and 15 
       msec. What is the prediction of the next time? (5 points)

  Ans: If take all four previous run times into consideration, the prediction
       is (((40 + 20) / 2 + 40) / 2 + 15) / 2 = ((30 + 40) / 2 + 15) /2
                                              = (35 + 15) / 2 = 25

       Or if take only two previous run times into consideration, the
       prediction is (40 + 15) /2 = 27.5