NO.PZ2023091701000057
问题如下：
If a pool of mortgage loans begins the month with a balance of $10,500,000, has a scheduled principal payment of $54,800, and ends the month with a balance of $9,800,000, what is the CPR for this mouth?
选项：
A.6.18%
B.42.24%
C.53.47% D.66.67%解释：
We use the following formulas: SMM = (prepayment/beg. bal – scheduled principal payment) and (1 – SMM)12 = (1 – CPR).
Prepayment = actual payment – scheduled payment = ($10,500,000 – $9,800,000) – $54,800 = $700,000 – $54,800 = $645,200
So: $645,200/($10,500,000 – $54,800) = 0.06177 and CPR = 1 – (1 – 0.06177)12 = 0.5347 = 53.47%
请教，算prepayment 时候，用总的payment 减去schedualed payment ，但schedualed payment 应该包括本金和利息吧，这里为什么只减本金？
