換題日 ---間隔天數

01/28/2012 --- 32

03/01/2012 --- 32

04/02/2012 --- 32

05/04/2012 --- 32

06/04/2012 --- 31

07/10/2012 --- 36

08/10/2012 --- 31

09/10/2012 --- 31

10/10/2012 --- 30

11/08/2012 --- 29

12/06/2012 --- 28

平均天數 --- 28.7