问题如下：
A Treasury bond pays coupons at the rate of 7% per year on June 1 and December 1. What is the accrued interest between June 1 and July 31 per USD 100 of face value?
解释：
The number of days between June 1 and December 1 is 183 (29, 31, 31, 30, 31, 30, 1 in June, July, August, September, October, November, and December, respectively). The number of days between June 1 and July 31 is 60 (29, 31 in June and July, respectively). The accrued interest is therefore:
3.5 x 60/183 = 1.1475
为什么是3.5不是7呢？不是yearly吗
