Wednesday, March 23, 2011

Okay, this may be the teeniest bit whiney, but...



I've been working diligently on my homework. Tuesday was 3 hours, and Monday was 1. I'm averaging something like 5 hours' work for each class session. When I get something wrong (I check my answers in the back of the book), I go over it again and again until I know how to come up with the right answer. I've done very very well with calculating interest rates. So how's come I can't get it right with the continuously compounded rate? Every single time, I get just a smidge off (like 11 to 13 cents off). I can't figure out what I'm doing wrong.




I blame Texas Instruments. Or I'd like to. This is how the machines take over, right? A bunch of pocket calculators, bored with the sheer inanity of their under-use, start talking to one another about how idiotic their handlers are and soon they'll be herding us into cattle cars or somesuch and whacking us on the palms with sapient pearwood slide-rules.




Okay. I know it's completely anal of me, but I want that last .25 percent of a point on my grade for my online homework. I'm scared later in the semester something will come along that's harder than what I've done so far, and then I'll need every jot and tittle of points to hold on to my A.




Can anyone tell me what I'm doing wrong? *vexation*

9 comments:

Dan said...

Just a question: are you carrying through all the way on the calculator or reentering some of the numbers? You need to be very careful how you handle it or the calculator will round a bit differently.

Jon said...

My solution to this type of assholery is to pull out some change and balance the figures. To an accountant, or other math wizard, this is blasphemy. Since math wizards control you destiny, you will have to get out the chicken bones and cast them daily to prevent a disaster.

phlegmfatale said...

Dan - I entered (on my TI-34) the formula exactly as demonstrated on the tutorial. In fact, in exasperation, I finally clicked the "help me solve this" button, and it laid out the formula. Actually, their formula had an e in it, and I couldn't figure out what that represented. *vex*

Jon - true. I may just have to take that hit and get these wrong. It's really frustrating because my work is consistent and so very, very close.

Christina LMT said...

Oh my gosh, I HATE seeing that red box pop up. SO FRUSTRATING.

North said...

Is there rounding happening in an intermediate step? Since this is 'money' there is nothing smaller than a cent.

If you are not rounding until the end, perhaps you shouldn't be. Or perhaps you should.

Try both ways. Try rounding to the cent (is that normal rounding, or always rounding up?) for each step to see if that has an effect on the final answer.

myspace_email said...

The "e" in the formula is Napier's number, the base of the Natural Logarithm (approx. 2.718282). If you are not using a sufficient number of decimal places for the approximation your result will be off. For example using 2.7182 I get a result of 11972.11.

Hope this Helps,

Steve

Anonymous said...

Okay, so I've been a lurker for a while, but I used to have a math brain, and I'm home on maternity leave, so I guess I'm trying to keep my brain from atrophying.

I did a search for continuously compounded interest, and found a link that calculates all the numbers you need. Looks like the number you came up with is not continuous, but rather almost continuous - seems to match the calculation for interest compounded by 365 days times 24 hours. I haven't looked at my TI for a long time, so I'm not sure what instructions to follow to actually get the integrated number, but maybe this will be a start.

http://www.moneychimp.com/articles/finworks/continuous_compounding.htm

Thanks for all your fun posts... back to lurking now...

Old NFO said...

Myspace beat me to it... Also, are you carrying to the second or third decimal place? I seem to remember that banks actually carry to the third decimal place...

Roscoe said...

Someone already pointed out that the value of e may not be correct. Are you entering 2.7182... manually or using the [e with tiny x] button on the calculator?

Depending on the vintage of the TI, the [e with tiny x] button may not be available and you use [INV][ln x] to do the calculation instead. My circa 1985 TI66 works that way.

Either way, talk to the instructor during office hours or after class if you're really bugged about the points.