SOLUTION: Here's another homework problem I am not sure how to do. The numbers don't seem to add up to one. Can someone please help and explain? Thanks for your help. Find the mean a

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Question 198460: Here's another homework problem I am not sure how to do. The numbers don't seem to add up to one. Can someone please help and explain? Thanks for your help.

Find the mean and standard deviation of the following probability distribution:
x | 1 2 3
P(x) | 0.4 0.15 0.35

Answer by stanbon(75887) (Show Source):
You can put this solution on YOUR website!
Here's another homework problem I am not sure how to do. The numbers don't seem to add up to one. Can someone please help and explain? Thanks for your help.
Find the mean and standard deviation of the following probability distribution:
x | 1 2 3
P(x) | 0.4 0.15 0.35
---------------------------------
OK, so it's not a probability distribution.
If it was a probability distribution the following would apply.
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mean = Sum[x*P(x)] = 1*0.4 + 2*0.15 + 3*0.35 = 1.75
--------
Variance = Sum[(x-u)^2 * P(x)]
= (1-1.75)^2*0.4 + (2-1.75)^2*0.15 + (3-1.75)^2*0.35
= 0.78125
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standard deviation = sqrt(variance) = 0.88388....
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Cheers,
Stan H.