Can you help me work out the variance?

• Feb 1st 2013, 02:36 PM
emily9843
Can you help me work out the variance?
I really need help on how to do the variance for this.

I know how to work out variance from a set of data and stuff, but the wording of this question is really confusing me. Could you please show all your steps so that I understand. Also I have changed one of the values so it is NOT the same as my homework, because I want to do that myself.... I just need someone to explain/show the steps. Thank you :)

Here are 10 values of a variable x. Find the variance using the coded values, u = x-20.

18.9 20.7 19.3 20.1 21.3 19.6 20.5 20.9 18.8 20.8

Thanks again
• Feb 1st 2013, 02:55 PM
chiro
Re: Can you help me work out the variance?
Hey emily9843.

Are you looking for the sample variance or are you treating this as a population?
• Feb 1st 2013, 03:03 PM
emily9843
Re: Can you help me work out the variance?
This one:

Variance = ( Σxifi / Σfi ) - (mean)^2
• Feb 1st 2013, 03:04 PM
emily9843
Re: Can you help me work out the variance?
I'm not sure what it's called lol but you can use it to work out standard deviation. I'm so stuck on this question. Thank you
• Feb 1st 2013, 03:09 PM
chiro
Re: Can you help me work out the variance?
I think your equation is wrong: check if xi should be xi^2 (i.e. xi squared) instead of xi.
• Feb 1st 2013, 03:12 PM
emily9843
Re: Can you help me work out the variance?
Oops, yes sorry I read it wrong on my sheet. Yes it is, do you know how to do this? :)
• Feb 1st 2013, 03:14 PM
chiro
Re: Can you help me work out the variance?
Basically you just plug the values into the formula.

The fi represents the number of times a particular xi occurs in your sample. In your example, it looks like everything occurs only once.
• Feb 1st 2013, 03:24 PM
emily9843
Re: Can you help me work out the variance?
what's the coded value, u = x-20 then? I'm sure that's not it :(
• Feb 1st 2013, 03:31 PM
chiro
Re: Can you help me work out the variance?
Is 20 the mean by any chance?
• Feb 1st 2013, 03:33 PM
emily9843
Re: Can you help me work out the variance?
no that's all the question asks, it's not the mean but i think you need to use it to work it out. so confused :( but don't worry
• Feb 1st 2013, 03:36 PM
chiro
Re: Can you help me work out the variance?
Just plug in the values of xi into the formula and calculate the variance. Don't worry about the u value since the variance doesn't change when you "shift" the values (like u = x - 20).