換題日 ---間隔天數

01/23/2008 --- 38

02/23/2008 --- 31

03/24/2008 --- 30

04/23/2008 --- 30

05/23/2008 --- 30

07/01/2008 --- 39

08/07/2008 --- 37

09/07/2008 --- 31

10/07/2008 --- 30

11/07/2008 --- 31

12/08/2008 --- 31

平均天數 --- 32.55