換題日 ---間隔天數

01/28/2011 --- 35

02/25/2011 --- 28

03/27/2011 --- 30

05/03/2011 --- 37

06/03/2011 --- 31

07/05/2011 --- 32

07/28/2011 --- 23

08/20/2011 --- 23

09/24/2011 --- 35

10/27/2011 --- 31

12/01/2011 --- 35

12/27/2011 --- 26

平均天數 --- 30.5