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Math Help - Tying to Find Variance and St Dev

  1. #1
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    Exclamation Tying to Find Variance and St Dev

    my variance is -2.37583E+12

    i need to find St Deviation but i cannot square root this number

    can someone help me change this number so i can put it under a square root?

    thanks
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  2. #2
    MHF Contributor harish21's Avatar
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    Firstly, you should know that variance is always non-negative. Here are some PROPERTIES if you want to have a look. So your proclaimed variance of
    -2.37583E+12 does not make any sense.

    Could you please post your actual question?
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  3. #3
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    But if we change the number, we will get the wrong result, won't we?

    You can't square root this number because it's a negative number. Negative numbers don't have square roots in real numbers. Are you sure your variance is correct?

    Sorry Harish, I started writing when there were no replies yet. I don't know how to delete this post.
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  4. #4
    MHF Contributor harish21's Avatar
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    Quote Originally Posted by ymar View Post
    But if we change the number, we will get the wrong result, won't we?

    You can't square root this number because it's a negative number. Negative numbers don't have square roots in real numbers. Are you sure your variance is correct?

    Sorry Harish, I started writing when there were no replies yet. I don't know how to delete this post.

    We cannot delete our own posts. Only Moderators can. It often happens that multiple number of people are replying to a post at the same time. Besides, your post is informative. So there is no need to delete it!!
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  5. #5
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    Code:
    x (cash prize $)	            P(x)	          X*P(X) 	            X2*P(X)
    15000000	                    6.8E-09	          0.102	                     1530000
    200000	                            0.00000028	          0.056	                     11200
    10000	                            0.000001711	          0.01711	             171.1
    100	                            0.000153996	          0.0153996	             1.53996
    7	                            0.004778961	          0.033452727                0.234169089
    4	                            0.007881463	          0.031525852                0.126103408
    3	                            0.01450116	          0.04350348	             0.13051044
    0	                            0.972682422	          0	                     0
    		                                          0.298991659	             1541373.131
    			
                                 Mean	      Variance	        St Dev	
                             0.2989917	      -2.37583E+12	?
    Last edited by CaptainBlack; February 10th 2011 at 06:40 PM.
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  6. #6
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    oh my goodness it squeshed all me data togeher sorry
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  7. #7
    Grand Panjandrum
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    Quote Originally Posted by Peyton Sawyer View Post
    Code:
    x (cash prize $)	            P(x)	          X*P(X) 	            X2*P(X)
    15000000	                    6.8E-09	          0.102	                     1530000
    200000	                            0.00000028	          0.056	                     11200
    10000	                            0.000001711	          0.01711	             171.1
    100	                            0.000153996	          0.0153996	             1.53996
    7	                            0.004778961	          0.033452727                0.234169089
    4	                            0.007881463	          0.031525852                0.126103408
    3	                            0.01450116	          0.04350348	             0.13051044
    0	                            0.972682422	          0	                     0
    		                                          0.298991659	             1541373.131
    			
                                 Mean	      Variance	        St Dev	
                             0.2989917	      -2.37583E+12	?
    You are using the wrong formula for the variance.

    Var(X)=E(x^2)-\overline{x}^2

    CB
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