disper

36.
Original mean :
(4 + 7 + 9 + 13 + 14 + x + y)/7 = 9
47 + x + y = 63
x + y = 16

New mean
= (4 + 7 + 13 + 14 + x + y)/6
= (4 + 7 + 13 + 14 + 16)/6
= 54/6
= 9

Original standard deviation :
√{[(4 - 9)² + (7 - 9)² + (9 - 9)² + (13 - 9)² + (14 - 9)² + (x - 9)² + (y - 9)²]/6} = 4
[(4 - 9)² + (7 - 9)² + 0² + (13 - 9)² + (14 - 9)² + (x - 9)² + (y - 9)²]/6 = 16
(4 - 9)² + (7 - 9)² + (13 - 9)² + (14 - 9)² + (x - 9)² + (y - 9)² = 96

New standard deviation
= √{[(4 - 9)² + (7 - 9)² + (13 - 9)² + (14 - 9)² + (x - 9)² + (y - 9)²]/5}
= √(96/5)
= √19.2

2012-05-09 23:54:52 補充：
Alternative method to find the mean :
Since mean is 9 and the removal of the datum "9: does not affect the mean,
thus new mean = 9