(12C) Mortgage Loan Interest Rate

[Albert Chan]

(06-15-2021 07:45 AM)Gamo Wrote:  [f] 2
36 [n]
3600 [PV]
360 [CHS] [PMT]
[i] ...... about 17 second display 9.64

To use program: same data as previous problem
press [R/S]....... about 12 second display 9.64

It seems HP12C use whatever was stored in [i] as guess.
If we provide same guess of program for HP12C TVM:

(-PMT/PV) - (-PV/PMT)/N² ≈ 1/10 - 10/36² ≈ 9.23%

9.23 [i] [i] ... finished in 10 second

Solve again, with true rate as guess

[i] [i] ... finished in 4 second

With 5% guess, and interrrupt rate search, we get this:

5 [i] [i] [On] [On]    → 8.99
   [i] [i] [On] [On]    → 9.62
   [i] [i] [On] [On]    → 9.64