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Calculate manually with RPN calculator
11-02-2019, 07:46 AM (This post was last modified: 11-02-2019 07:58 AM by Stevetuc.)
Post: #10
RE: Calculate manually with RPN calculator
(10-31-2019 05:13 AM)Gamo Wrote:  Manually calculate the Interest Rate for an Annuity.

Formula use to solve for [ i ] the interest rate when these three variables are known.

n - Period
PV - Present Value
PMT - Payment

f(i) = (PMT ÷ PV) + [ i ÷ 1 - (1+i)^n ]

———————————————————-

Steps: FIX 4

Setup: n [STO] 0 PMT [ENTER] PV [÷] [ENTER] [ENTER] [ENTER] [.] 1

Iterations: [ENTER] [ENTER] 1 [+] [RCL] 0 [Y^X] 1 [-] [÷] [-]

———————————————————-
Example: n = 25, PV = 2000, PMT = 203.61, i = ?

Using HP-12C result is 8.9998 or i = 9%

On the original HP-12C when calculate step to [Y^X] the screen will turn blank momentary.
and resume normal operation.

Calculate Manually:

25 [STO] 0 203.61 [ENTER] 2000 [÷] display 0.1018 [ENTER] [ENTER] [ENTER] . 1

[ENTER] [ENTER] 1 [+] [RCL] 0 [Y^X] 1 [-] [÷] [-] display 0.0916

[ENTER] [ENTER] 1 [+] [RCL] 0 [Y^X] 1 [-] [÷] [-] display 0.0903

[ENTER] [ENTER] 1 [+] [RCL] 0 [Y^X] 1 [-] [÷] [-] display 0.0900

[ENTER] [ENTER] 1 [+] [RCL] 0 [Y^X] 1 [-] [÷] [-] display 0.0900

Last two iterations got the same value based on 4 decimal places.

[EEX] 2 [x] display 9

Answer: 9%

———————————————————————————-
Note: The [.] 1 is a guess
Hint: For higher decimal place accuracy simply do more iterations.
———————————————————————————

Gamo

This works on the prime too, with some modification;
First set to fixed 4 and assuming home set to rpn mode:

1'HFormat' [SHIFT STO]
4 'HDigits' [SHIFT STO]

25'X' [SHIFT STO] 203.61 [SPACE or ENTER] 2000 [÷] display 0.1018 [ENTER] [ENTER] [ENTER] .1

[ENTER] [ENTER] 1 [+] X [X^Y] 1 [-] [÷] [-] display 0.0916

Etc..
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RE: Calculate manually with RPN calculator - Stevetuc - 11-02-2019 07:46 AM



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