This math problem is vexing me...I'm getting old and stupid(er)
any takers?
500(1.05)^x/4=200
The (1.05) is raised to the "x over 4" power...
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| Author: | L. Presnall [ Thu Aug 10, 2006 3:32 pm ] |
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This math problem is vexing me...I'm getting old and stupid(er) any takers?
500(1.05)^x/4=200 The (1.05) is raised to the "x over 4" power... |
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| Author: | letseatpaste [ Thu Aug 10, 2006 4:30 pm ] |
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My math skills are rough, but I get x=-75.121 500(1.05)^(x/4)=200 (1.05)^(x/4)=.4 [(1.05)^(1/4)]^x=.4 1.012^x=.4 x=log(.4, base=1.012) x=log(.4) / log(1.012) x=-75.221 I had to take a little wikipedia logarithm refresher course, but I think that's it. Set it up in Mathcad, so it's taking into account a lot more decimal places that I'm showing here. |
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| Author: | Serge Poirier [ Thu Aug 10, 2006 10:20 pm ] |
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I'm gonna make a boat drawing! 
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| Author: | Jeanne [ Thu Aug 10, 2006 11:34 pm ] |
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Now Serge, this just looks confusing to you because it's not metric 
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| Author: | L. Presnall [ Fri Aug 11, 2006 1:03 am ] |
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Paste, YOUDA MAN!  I have my kid's TI-83, which would take longer to learn than the stinking aircraft I'm training on!!
Serge, the boat drawing I could actually help with! |
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| Author: | L. Presnall [ Fri Aug 11, 2006 2:06 am ] |
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3^2x-5=13
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| Author: | letseatpaste [ Fri Aug 11, 2006 2:35 am ] |
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Is it 3^(2x-5) or 3^(2x) - 5? You're not cheating on homework are you? :) |
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| Author: | letseatpaste [ Fri Aug 11, 2006 2:39 am ] |
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3^(2x-5) = 13 2x-5 = log(13, base 3) 2x-5 = log(13) / log(3) 2x-5 = 2.335 2x = 7.335 x = 3.668 |
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| Author: | L. Presnall [ Fri Aug 11, 2006 3:23 am ] |
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[QUOTE=letseatpaste] Is it 3^(2x-5) or 3^(2x) - 5? You're not cheating on homework are you? :)[/QUOTE] Not yet!
Just working backwards to try and figure out this danged TI-83!! 
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| Author: | letseatpaste [ Fri Aug 11, 2006 3:25 am ] |
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I've got the TI-81, we had to use them for pre-calc in highschool, the textbook was based on it. I don't know anything about the 83, or if they're even similar. |
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| Author: | L. Presnall [ Fri Aug 11, 2006 3:26 am ] |
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Okay Paste, but how does a guy change base with the stupid calculator!!!!
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| Author: | letseatpaste [ Fri Aug 11, 2006 3:35 am ] |
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I couldn't figure out a way to change base on my calculator... you do it by turning it into a ratio of logarithms like I did above... log(x) with base=b is the same as log(x) / log(b) (base=10, which is default on calculators). The base doesn't matter in the ratio, so you could use natural log (ln) in the same way. Mathcad lets you change the base, I'm sure Excel probably does, too, but I don't think most calculators will. With the above method, you can use any cheapo scientific calculator. Fun to flex my brain a bit. I do engineering, but most of my calcs are the same thing over and over. |
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| Author: | Serge Poirier [ Fri Aug 11, 2006 4:10 am ] |
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[QUOTE=Jeanne] Now Serge, this just looks confusing to you because it's not metric [/QUOTE]
No Jeanne, i'm metrically and imperially easily confused! Do we need to calculate and measure stuff for real around here?
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| Author: | Serge Poirier [ Fri Aug 11, 2006 4:11 am ] |
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[QUOTE=L. Presnall] Serge, the boat drawing I could actually help with! [/QUOTE] Great, i'll let you do the measuring! ok?
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| Author: | L. Presnall [ Fri Aug 11, 2006 4:44 am ] |
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paste, my brain doesn't flex so easily anymore!!
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| Author: | letseatpaste [ Fri Aug 11, 2006 5:12 am ] |
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Wikipedia, it's the new Google... Wikipedia on logarithms Check section 1.2, change of base. 
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| Author: | old man [ Fri Aug 11, 2006 8:57 am ] |
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Why don't you make it over to Bruce's on the 19th for the Arkansas gathering? Jon (paste) will be there, and we can all have a math discussion and play music.
Aren't you in Memphis? Jimmie Sorrells is comint from Memphis. Ron |
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| Author: | Serge Poirier [ Fri Aug 11, 2006 3:37 pm ] |
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I'd sure love to go to Bruce's too. For music that is, not math!
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