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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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http://www.presnallguitars.com

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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Jonathan Kendall, Siloam Springs AR

I'm gonna make a boat drawing!

Now Serge, this just looks confusing to you because it's not metric

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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http://www.presnallguitars.com

3^2x-5=13

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http://www.presnallguitars.com

Is it 3^(2x-5) or 3^(2x) - 5?

You're not cheating on homework are you? :)

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Jonathan Kendall, Siloam Springs AR

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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Jonathan Kendall, Siloam Springs AR

[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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http://www.presnallguitars.com

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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Jonathan Kendall, Siloam Springs AR

Okay Paste, but how does a guy change base with the stupid calculator!!!!

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http://www.presnallguitars.com

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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Jonathan Kendall, Siloam Springs AR

[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?

[QUOTE=L. Presnall]
Serge, the boat drawing I could actually help with! [/QUOTE]

Great, i'll let you do the measuring! ok?

paste, my brain doesn't flex so easily anymore!!   

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http://www.presnallguitars.com

Wikipedia, it's the new Google...

Wikipedia on logarithms

Check section 1.2, change of base.

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Jonathan Kendall, Siloam Springs AR

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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OLD MAN formerly (and formally) known as:

Ron Wisdom

Somewhere in the middle of Arkansas......

I'd sure love to go to Bruce's too. For music that is, not math!