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Finding the mean and standard deviation from an equation with sigma

IBstudent

New member
Joined
Jan 27, 2012
Messages
36
math problem.jpg
I have been having some trouble solving a specific problem asking to find the mean and standard deviation of a population when given two equations with sigma (see attached)

My attempt was to find x so that x + (x+1) + (x+2) + ....... + (x+24) = 300. So 25x + 300 = 300... wait... then x is zero...

Am I doing it wrong? please explain this to me I'm lost :S

Also, how is it possible to get the standard deviaiton from such equation?

Please don't leave comments like "go back to your textbook", I have and it says nothing about this...

Thanks in advance
 

galactus

Super Moderator
Staff member
Joined
Sep 28, 2005
Messages
7,216
The populations sums to 300 and there are 25 of them. Looks like the mean would be

\(\displaystyle \frac{300}{25}=12\)
 

IBstudent

New member
Joined
Jan 27, 2012
Messages
36
The populations sums to 300 and there are 25 of them. Looks like the mean would be

\(\displaystyle \frac{300}{25}=12\)
Thanks.. now I understand this bit
What about the second bit?
 
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