換題日 ---間隔天數

01/07/2009 --- 30

01/27/2009 --- 20

03/02/2009 --- 34

04/07/2009 --- 36

05/04/2009 --- 27

06/09/2009 --- 36

07/17/2009 --- 38

08/21/2009 --- 35

09/24/2009 --- 34

10/21/2009 --- 27

11/18/2009 --- 28

12/07/2009 --- 19

平均天數 --- 30.33