HP 12c Platinum TMV help « Next Oldest | Next Newest »

 ▼ Brandony Junior Member Posts: 2 Threads: 1 Joined: Jan 1970 01-24-2008, 03:36 PM I have just purchased a 12c calc. I am having trouble with one particular par t of TMV calculations. When I am trying to figure out n (number of years) the calculator automatically rounds up to the next higher number. I understand why it does this with certain applications of TMV but I need it to display actual time. For instance I am trying to figure out how much time it takes to get to a FV when I have a specific PV and interest rate. It always round the number to the next highest year. Is there a way to get the calculator to display actual years (3.02 years)??? ▼ Gene Wright Posting Freak Posts: 1,545 Threads: 168 Joined: Jul 2005 01-24-2008, 03:56 PM No. Sorry. The users guide has a procedure you can use to estimate the fractional part of n. It is found on pages 63 through 68. This was a design choice made by the original 12c team long long ago. ▼ Steve Perkins Member Posts: 104 Threads: 0 Joined: Dec 2007 01-24-2008, 06:26 PM The 12-C can't do this with the built-in TVM functions, but your specific problem seems easy to solve. I believe the simple formula for compound interest is: FV = PV * (1 + i) ^ n Here n is the number of periods, and i is the interest rate per period expressed as a decimal. So 6% annual interest (compounded annually) gives: FV = PV * (1.06) ^ n If you want to do monthly compounding, divide the .06 by 12, and multiply n by 12. Now using logarithms we can solve for the exponent n. ln(FV) = ln (PV * (1.06) ^ n) = n * ln (PV * (1.06)) so n = ln (FV) / ln (PV * (1.06)) Hope I didn't mess up my formula, algebra, or explanation too badly. ▼ tony (nz) Member Posts: 93 Threads: 2 Joined: Jul 2005 01-24-2008, 06:58 PM n=ln(FV/PV)/ln(1.06) ? ▼ Steve Perkins Member Posts: 104 Threads: 0 Joined: Dec 2007 01-24-2008, 07:25 PM You're right, Tony. The PV isn't part of the value raised to the power of n, so your solution is correct. Thanks! ▼ Brandony Junior Member Posts: 2 Threads: 1 Joined: Jan 1970 01-24-2008, 07:41 PM Thanks guys, You are right on the equation. I know that is one way to do it ( I was a math major) I was just curious if the 12c could do that function for me. Thank you all for a good speedy response. Allen Senior Member Posts: 562 Threads: 27 Joined: Oct 2006 01-24-2008, 08:19 PM FWIW, Neither the 17bii nor the 48G TVM solvers have the 12C rounding issue. Edited: 24 Jan 2008, 8:37 p.m. ▼ Gene Wright Posting Freak Posts: 1,545 Threads: 168 Joined: Jul 2005 01-24-2008, 09:44 PM (* Edited to correct to monthly example rather than annual *) An exact value for N in these circumstances may be mathematically correct, but meaningless in reality. For example, the question: How many MONTHLY deposits of \$100 does it take into an account paying 6% compounded monthly before you have accumulated \$5,000? (Assuming payments made at the end of a period. The exact answer for N that many calculators give is 44.7402.... However, the real answer is that it takes 45 deposits of \$100 under these circumstances. You can't have .7402 of a \$100 deposit. You either make a deposit of \$100 or you don't. After 44 deposits, you would have less than \$5,000. At 45, you have more than \$5,000. No integer number of deposits will give you exactly \$5,000. Therein lies the problem. 44.74... makes the formula work to equal the \$5,000, but, IMO, it is a malformed question. The 12c designers choose the "real" approach. Other calculator models (and manufacturers) choose the mathematically correct solution. That is why the confusion exists. When I teach this type of stuff at the university, I usually pose the questions like this: "How many deposits...before you would have at least \$5,000 in the account?" The answer would be 45 in this set of circumstances. 44.74... if returned would be rounded up by thinking the issue through. My 2 cents (which doesn't buy much these days) Gene Edited: 25 Jan 2008, 8:09 a.m. after one or more responses were posted ▼ Kareem Mokdad Junior Member Posts: 12 Threads: 0 Joined: Jan 2008 01-25-2008, 03:37 AM Hi Gene, I just tested your last example on my 17BII+, the answer for N it returns is 44.74. Any idea why? ▼ Gene Wright Posting Freak Posts: 1,545 Threads: 168 Joined: Jul 2005 01-25-2008, 08:10 AM The 17b2+ returns the mathematically correct value for N. It solves for N differently than the 12c. Peter A. Gebhardt Member Posts: 174 Threads: 20 Joined: Sep 2006 01-25-2008, 04:41 AM Gene, I think you've meant "monthly" ;-) Quote: How many annual deposits of \$100 does it take ... Best regards, Peter A. Gebhardt Edited: 25 Jan 2008, 4:43 a.m. ▼ Gene Wright Posting Freak Posts: 1,545 Threads: 168 Joined: Jul 2005 01-25-2008, 08:08 AM Oops. Bad day for me all around. :-) Mad Dog ebaycalcnut Member Posts: 124 Threads: 17 Joined: Dec 2006 01-26-2008, 05:29 PM How about the 48G+ ? ▼ Gene Wright Posting Freak Posts: 1,545 Threads: 168 Joined: Jul 2005 01-26-2008, 08:50 PM No need to search any longer. The 12c designers took the practical approach. Doesn't seem to have hurt sales over the last 25 years. :-) Peter A. Gebhardt Member Posts: 174 Threads: 20 Joined: Sep 2006 01-25-2008, 06:31 AM Brandony, Pls. be aware that so called "Usances" (usages or special regulations for the calculation of interest) exist in different jurisdictions and/or for different financial instruments. As a reference look at: were exceptions are described, where and when to use "simple interest" calculations. So the implementation of TVM in the HP-12c makes perfectly sense for someone used to divide the total accumulated interest into interest from periods with compounded and such of simple interest respectively. Wether if it's easier to calculate the simple interest part by the HP-12c method or from the fractional result of the HP-17b (and its siblings) is left to anybody's preference. Best regards Peter A. Gebhardt Edited: 25 Jan 2008, 9:42 a.m.

 Possibly Related Threads... Thread Author Replies Views Last Post HP 12C Platinum Programming v. Gold Face Dean Lewis 10 1,462 11-03-2013, 07:30 PM Last Post: Kimberly Thompson HP12C Platinum PC software activation fails Russell Clinton 0 518 07-02-2013, 02:32 PM Last Post: Russell Clinton HP 12c Platinum Emulator Activation Server Problem Danny Farley 5 798 04-09-2013, 09:13 PM Last Post: Danny Farley Good deal : HP 12c Platinum for half-price Mic 1 605 01-21-2013, 03:51 AM Last Post: Vincent Guilbault Simple financial problem with a HP-12c Platinum Lapin 3 699 11-11-2012, 09:33 AM Last Post: Lapin Confused simple accountant: TMV HP17 v HP12 Paul 4 651 09-17-2011, 10:12 AM Last Post: Paul HP 12C Platinum CHS bug? M. Joury 23 2,285 08-11-2011, 06:45 PM Last Post: Gerson W. Barbosa HP 12C, 12C Platinum & 15C iOS App Walter Lam 2 586 06-02-2011, 01:25 PM Last Post: Andrés C. Rodríguez (Argentina) Calculator for CFA; HP 12C Platinum or TI BA II Plus Professional Sujith Abraham 23 2,371 03-22-2011, 11:46 PM Last Post: Martin Pinckney Self tests in the HP12C Platinum+ Jose Ernesto 3 669 02-08-2011, 02:31 PM Last Post: Lyuka

Forum Jump: