(11C) TVM for Interest Rates Solutions

[Gamo]

This Interest Rate Solver solutions is based on program provided by
HP-55 Mathematics Programs handbook.

Procedure:

Input n (Periods in days, month or year) [A] // This step must be enter for all problem below

Use PV and PMT: Input PV [ENTER] PMT [B] display interest rate in percent

Use FV and PMT: Input FV [ENTER] PMT [C] display interest rate in percent

Use PV and FV: Input FV [ENTER] PV [D] display interest rate in percent

Solve for PMT: Input Interest [E] input PV [R/S] display Payment amount
----------------------------------------------
Example: USER FIX 2

"Payment Method is Ordinary Annuities (End Mode)"

n, PV/PMT for 12, 5000/500
12 [A] 5000 [ENTER] 500 [B] display brieftly the suggest guess 3.06 then 2.92%

n, FV/PMT for 12, 5000/400
12 [A] 5000 [ENTER] 400 [C] display brieftly the suggest guess 0.75 then 0.74%

n, FV, PV for 60, 3000/2000
60 [A] 3000 [ENTER] 2000 [D] no guess needed then answer 0.68%

n, i, PV for 180, 6%, 200000
180 [A] 6 [E] display 0.01 Input 200000 [R/S] display payment answer 1687.71
-------------------------------------------
Program:

Code:


LBL A  // input periods
STO 1
RTN
------------------------------------
LBL B  // problem for n, PV, PMT
÷ STO3 1/x RCL1 X^2 1/x RCL3 x - STO2 GSB2 PSE
LBL 0
RCL3 RCL2 x 1 RCL2 1 + RCL1 CHS Y^X STO5 - -  RCL1 RCL2 1/x 1 + ÷ 1 +
RCL5 x 1 - GSB3 EEX12 CHS X≤Y GTO 0 RCL2 GTO 2
------------------------------------- 
LBL C  // problem for n, FV, PMT
÷ STO3 RCL1 - 2 x RCL1 1 - X^2 RCL3 + ÷ STO2 GSB2 PSE
LBL 1
RCL 3 RCL2 x 1 + RCL2 1 + RCL1 Y^X STO4 - RCL1 1 RCL2 1/x + ÷
1 - RCL4 x 1 + GSB3 EEX CHS 12 X≤Y GTO1 RCL2 GTO2
------------------------------------
LBL D  // problem for n, FV, PV
÷ RCL1 1/x Y^X 1 - 
LBL 2
EEX2 x RTN
LBL 3
RCL2 ÷ ÷ STO+2 X^2 RTN
-----------------------------------
LBL E  // Problem to solve for Payment with known n, i, PV
EEX2 ÷ 12 ÷ STO2 R/S
STO3 RCL2 1 RCL2 1 + RCL1 CHS Y^X - ÷ RCL3 x RTN

Remark:
Problem from Labels [B] and [C] use the Suggested Guess to find Interest Rate
from HP-55 handbook.

Label [B] for PV/PMT used this formula for suggested guess
[1 / (PV / PMT)] - [(1 / n^2) x (PV / PMT)]

Lable [C] for FV/PMT used this formula for suggested guess
[((FV/PMT) - n) x 2] ÷ [(n - 1)^2 + (FV/PMT)]

Gamo 2/2020