# Finding the mean and standard deviation from an equation with sigma

#### IBstudent

##### New member

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
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
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?