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Expected value, variance, standard deviation (FREE STICKERS)

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lands11
Posts: 1818 - Karma: 1,677
Ok NS so I have been asking for a ton of help on math problems lately. So since I really have appreciated it I will mail stickers to whoever can correctly answer this problem(s) first and show the steps.

Expected value, variance, and standard deviation
I need to find all three for 1/9x^(2/3), 1≤x≤8. (that is 1 over 9x^(2/3))

Please show your steps as you go, thank you.


Jun 17 2011 2:31PM
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lands11
Posts: 1818 - Karma: 1,677
Doesn't really help, thanks for trying though!
Jun 17 2011 2:43PM
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MN_Nice
Posts: 3824 - Karma: 56
Summer school. lololololololol
Jun 17 2011 2:44PM
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lands11
Posts: 1818 - Karma: 1,677
online calc 2 so I can get ahead
Jun 17 2011 2:51PM
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fdsa
Posts: 686 - Karma: 19
Expected value = integral from 1 to 8 - if you can't integrate this function, you deserve to fail so I'm not doing that part for you.

Variance = mean of the equare - square of the mean. So, square the whole function and integrate like you did above. Next, square the value you got from part 1, and subtract the two. Integration? See above.

Standard deviation = square root of the variance.

Jun 17 2011 2:56PM
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lands11
Posts: 1818 - Karma: 1,677
For expected value don't you need to put in an extra x at the beginning og the equation before you integrate?
Jun 17 2011 3:06PM
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deleted5
Posts: 14507 - Karma: 13,500
nope
Jun 17 2011 3:07PM
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fdsa
Posts: 686 - Karma: 19
Right you are sir. so instead of integrating 9x^-(2/3) you will be integrating 9x^(1/3)
Jun 17 2011 3:08PM
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fdsa
Posts: 686 - Karma: 19
http://www.ltcconline.net/greenl/courses/117/DoubIntProb/ExpValVariance.htm

Yes you do. Have you even had calc II?
Jun 17 2011 3:08PM
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lands11
Posts: 1818 - Karma: 1,677
In my book they keep multiplying the entire function by x, that's what is throwing me off. Here is an example in the book f(x)=(3/26)x^2 on [1/3) then when they start to find expected value then integrate x(3/26x^2)dx. Where did that x in the front come from?
Jun 17 2011 3:12PM
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lands11
Posts: 1818 - Karma: 1,677
Oh nice thanks man, well since you have helped me the most you can pm me your address and I'll send you some stickers. I have a shit ton, Saga die-cuts I think a few oakley die-cuts. Some black salomon die cuts oh and gold ones too. I have a shit ton
Jun 17 2011 3:14PM
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panojibber
Posts: 3382 - Karma: 216
I may have done this at some point, but if I did I don't remember it.
http://www.wolframalpha.com/

Thats all I've got.
Jun 17 2011 3:15PM
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fdsa
Posts: 686 - Karma: 19
Don't sweat it. Remember when you go to find the variance don't forget to square 9x^(1/3). Since it's a simple function though, it won't significantly complicate the problem.

GL with summer school. I took Calc II in the summer years ago. It wasn't so bad.

Props for staying on the ball over the summer.
Jun 17 2011 3:17PM
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lands11
Posts: 1818 - Karma: 1,677
Alright thanks for your help, It was very much appreciated.
Jun 17 2011 3:20PM
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deleted5
Posts: 14507 - Karma: 13,500
my dad whos a mathematician doesn't understand your questions. he put it in a graph with a curve and want to know if you want the value for 1.001-7.999. or the value of real numbers.
Jun 17 2011 3:22PM
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fdsa
Posts: 686 - Karma: 19
He's looking for the values of mean, variance, and standard deviation on the interval from 1 to 8 over all real numbers between the two, which is an infinitely large number of real numbers.
Jun 17 2011 3:28PM
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JakeAssBeatClap
Posts: 6673 - Karma: 2,535
The definition of a mathematician is a person skilled or learned in mathematics. So I'm also a mathematician and I say you're gay.
Jun 17 2011 3:29PM
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deleted5
Posts: 14507 - Karma: 13,500
Good one man you got me good.
Jun 17 2011 3:57PM
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dilla_says_go
Posts: 5333 - Karma: 168
http://en.wikipedia.org/wiki/Expected_value
Jun 17 2011 5:07PM
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