12c Solving for n - Printable Version +- HP Forums (https://www.hpmuseum.org/forum) +-- Forum: HP Calculators (and very old HP Computers) (/forum-3.html) +--- Forum: General Forum (/forum-4.html) +--- Thread: 12c Solving for n (/thread-8729.html) 12c Solving for n - Zac Bruce - 07-24-2017 11:27 AM Hi all, I'm hoping someone can lend their wisdom here. As most of you will well know, when using the 12c to solve for n, it will only solve as an integer, always rounding up. I tried to search but did not come across a solution. The user manual offers the following solution for when a PMT amount is involved; 10.5 g i 35000 PV 325 CHS PMT n (=328) To find the partial last payment; FV (181.89) RCL PMT (-325) + (-143.11) which is the final fractional payment To then make the answer correlate with other financial calculators I came up with the following; (with the -143.11 still on screen) RCL PMT X> 328 327 n PV => 34991,78 35000 – PV 0 PMT 328 n FV => 143,11 OK, that's a lot more complicated. #-) (07-25-2017 10:52 AM)Zac Bruce Wrote:  In place of my original approximate solution (n=327.44), it would instead be interpreted as "327 full payments of $325, plus a final payment of$143.11" and not in terms of time. I'd say that your approximate result of n=327,4403 may be interpreted as 327,4403 payments, i.e. 327 full and one final payment of 0,4403... times $325 =$143,11. (07-25-2017 10:52 AM)Zac Bruce Wrote:  The site that Paul suggested included a program to solve for a mathematically correct value of n, which is slightly different to your suggestion (allows for END or BEGIN by storing 1 in either STO 1 or STO 2) but comes up with the same results. Yes, my little program does only a very basic calculation for this particular case. Real TVM programs do a lot more stuff. ;-) On the other hand the HP-41 standard pac's TVM program (cf. line 06...20) shows how various scenarios (OK, END mode only) can be handled with one simple formula for n. Here is a translation for the 12C: Code: 01 RCL FV 02 CHS 03 RCL PMT 04 RCL i 05 / 06 EEX 07 2 08 x 09 + 10 RCL PV 11 LstX 12 + 13 / 14 LN 15 1 16 RCL i 17 % 18 + 19 LN 20 / 21 GTO 00 (07-25-2017 10:52 AM)Zac Bruce Wrote:  I guess if I do the work to internalize and memorize the equation, then yes, very simple! I'm perhaps too blessed to have constant access to electronics and the internet to do the "hard" work for me! C'mon, this compound interest formula is as basic at it gets. ;-) (07-25-2017 10:52 AM)Zac Bruce Wrote:  I bought a copy of Gene Wright's book, I think I might go and get it printed and bound tomorrow, start reading and try actually understand the maths, rather than just understanding which buttons to press! I think there are three levels involved here: (0) Knowing which buttons to press (1) Knowing the math behind this (2) Knowing the meaning of the math. ;-) Regarding the latter I'm sometimes a bit lost myself. Dieter RE: 12c Solving for n - Zac Bruce - 07-27-2017 12:19 PM Dieter, I've made some progress through Gene's book now, and you're right about it being pretty simple. My math is not strong so I didn't know that the log of a number to a power is equal to the power multiplied by the log of that number. What a mouthful. Gene does offer a quick and dirty way to approximate, but it's really no simpler than just working through the formula. I still don't understand was a logarithm really is, but at least compound interest is starting to make sense. So I guess I'm at stage two, at least! Regards, Zac RE: 12c Solving for n - Dieter - 07-27-2017 07:00 PM (07-27-2017 12:19 PM)Zac Bruce Wrote:  My math is not strong so I didn't know that the log of a number to a power is equal to the power multiplied by the log of that number. What a mouthful. (...) I still don't understand was a logarithm really is, but at least compound interest is starting to make sense. Power and exponential functions as well as their inverses (roots and logs) are basic math that is not too hard to understand. If it can be done at school in grade 8 or 9 you will be able to get it as well. All this stuff is required to understand the concept of the time value of money, both in simple compoud interest problems, in annuities and in other basic concepts like NPV or IRR. So every minute you spend on this for a better understanding of these basics will pay off later. Financial math simply is not possible without this. There is a reason why the 12C has only a few scientific functions while it does have y^x, e^x and ln x. ;-) Dieter RE: 12c Solving for n - Zac Bruce - 07-27-2017 09:40 PM Dieter, When I tell people that I'm studying accounting/finance, usually the first question I get asked is, "Are you good at maths? (sic)". Usually I just laugh and say, "Yeah." The truth being that I'm very systematic and I enjoy processes and logic. So, I would have been good at math if only I'd been paying more attention! I took advanced math in year 10, but I don't remember ever bringing my notebook or doing exercises. I did pass, but I remember very little. Last trimester I did my first statistics for business course and really enjoyed it, and topped my class. The math involved in (basic) probabilities and statistics is not so difficult to understand. But I realize that I lack any strong foundation, so I'm currently doing a self-paced bridging course offered by my university. Then it's on to quantitative skills with applications, which covers logarithmic, exponential and inverse functions in greater detail, among other things. Regards, Zac