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#1 2010-02-21 08:26:33
- Skromnaya
- Member
- Registered: 2010-02-21
- Posts: 24
Help with standard deviation=/
i am a bit confused on how to do the standard deviation of a set of numbers.
For example:
3,24,30,47,43,7,47,13,44,39
how do i find the standard deviation for those numbers?
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#2 2010-02-21 08:34:33
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Hi Skromnaya;
Do you know the formula?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#3 2010-02-21 08:36:46
- Skromnaya
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Re: Help with standard deviation=/
I think so.
Its
square root of (x-mean)squared over n-1.
I subtracted the mean from each number and squared the answers for each,then i added all of the square roots of each number and i dont know what to do next.
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#4 2010-02-21 08:39:11
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Hi;
What did you get for the mean?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#5 2010-02-21 08:43:16
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
29.7
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#6 2010-02-21 08:47:40
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Hi;
What did you get for the each point minus the mean?
Did you get this:
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#7 2010-02-21 08:53:52
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
3-29.7=(-26.7)squared=712.89
24-29.7=32.49
30-29.7=0.09
47-29.7=299.29
43-29.7=176.89
7-29.7=515.29
47-29.7=299.29
13-29.7=278.89
44-29.7=204.49
39-29.7=8.49
and the total for all those numbers is 2528.1
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#8 2010-02-21 08:56:03
- Skromnaya
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- Posts: 24
Re: Help with standard deviation=/
actually yes i got all those numbers,but i posted the numbers i got after finding the square root of the numbers you posted
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#9 2010-02-21 08:59:29
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Hi;
The last one is wrong. Check your work (39-29.7)^2 doesn't equal 8.49
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#10 2010-02-21 09:02:45
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
oh,i got 86.49.Thanks.Im just having trouble filling in the formula with the right numbers.
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#11 2010-02-21 09:05:16
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
The next step is the hardest. Is your data the whole population or a sample from a population?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#12 2010-02-21 09:06:09
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
the whole population
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#13 2010-02-21 09:07:38
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Hi;
Then your formula should divide by n not n-1
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#14 2010-02-21 09:12:11
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
ohhh ok
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#15 2010-02-21 09:14:55
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
how about if it was for the sample population?what would the formula be?
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#16 2010-02-21 09:15:09
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Whoa, wait a second. What does the formula you are using have as the denominator? This is important to get the right answer. Does it look something like my post # 13?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#17 2010-02-21 09:20:08
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
we only talked about this formula in class.
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#18 2010-02-21 09:21:53
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Excellent! Is that the formula that you are expected to use? The one your teacher has been using for these type of problems?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#19 2010-02-21 09:23:01
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
yes
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#20 2010-02-21 09:24:02
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
after putting in all the number into the formula i got 286.27.Im just not sure if it's right.=/
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#21 2010-02-21 09:26:18
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Ok, did you divide by 9 and what did you get in the numerator?
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#22 2010-02-21 09:27:40
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
i got 2576.4/9=286.27
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#23 2010-02-21 09:28:28
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
That's wrong. Please do it again.
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
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#24 2010-02-21 09:30:26
- Skromnaya
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- Registered: 2010-02-21
- Posts: 24
Re: Help with standard deviation=/
i got 286.2666 so i rounded it to 286.27
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#25 2010-02-21 09:32:04
- bobbym
- bumpkin
- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606
Re: Help with standard deviation=/
Can I see the list you are adding because I think you are supposed to get 2606.1
In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.
Offline