# Thread: Tying to Find Variance and St Dev

1. ## 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

2. 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.

3. 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.

4. Originally Posted by ymar
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!!

5. Code:
x (cash prize $) P(x) X*P(X) X2*P(X) 15000000 6.8E-09 0.102 1530000 200000 0.00000028 0.056 11200 10000 0.000001711 0.01711 171.1 100 0.000153996 0.0153996 1.53996 7 0.004778961 0.033452727 0.234169089 4 0.007881463 0.031525852 0.126103408 3 0.01450116 0.04350348 0.13051044 0 0.972682422 0 0 0.298991659 1541373.131 Mean Variance St Dev 0.2989917 -2.37583E+12 ? 6. oh my goodness it squeshed all me data togeher sorry 7. Originally Posted by Peyton Sawyer Code: x (cash prize$)	            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