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Full Version: "A Penny for your thoughts" on the HP50g
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Hello,

My apologies if this has been brought up previously. I have tried searching the archives for TVM, penny and HP50g, but with no obviously relevant hits.

The brilliant paper "Mathematics written in sand" by W. Kahan contains the example TVM problem "A penny for your thoughts", wherein it is computed the value of a penny deposited every second for a year into an account of 10% annual interest, compounded every second.

The correct answer, according to the paper, is 331667.0067 dollars. This is also the result obtained by Tommi's TVM solver program for the HP42s posted on this site in 2005 (and this problem is one of the examples used in that posting.)

The HP50g TVM application gives me the answer 541877.3438, which is so far off the mark that I suspect I must be doing something wrong.

I'm setting variables as follows:

```n = 3600*24*365 = 31536000
I%YR = 10/n = 3.17097919838e-6
PV = 0
PMT = -0.01
P/YR = 1
End mode
```

Solving for FV gives the above 514877.3438 as result.

Tips?

--Tom G

I fear you have made a small mistake. From Prof. Kahan's article, page 15/49:

``` n := 60*60*24*365 = 31,536,000 sec. per year.
i := 10/n = 0.000 000 317 097 9198 % per sec.
PV := 0
PMT := -0.01 = one cent per sec. to the bank.
```
that is,

i := 3.17 097 9198e-7 % per second, not 3.17 097 9198e-6 as you have used.

This will give you 331 667.006 691 dollars.

Gerson.

D'oh!

Thanks!

Just for kicks, after I entered YOUR numbers, I got an approx. FV of 541 thousand, not 514 thousand. Typo?