Standard deviation help

donald_duck

New member
Joined
Jan 5, 2021
Messages
1
Hello,

I'm really hoping someone can help me with standard deviation for grouped data. I have read the formula and tried several problems but it just doesn't click.

If I need to calculate a standard deviation of the number of cars in households, what is the correct way to do it?

0 cars - 1635 households
1 car - 2800 households
2 cars - 2410 households

Your help would be much appreciated!
 
Mean = sum x * pr(x) -- x = 0, 1, 2
Variance = sum x^2 * pr(x)

Your challenge is to find the probabilities.

You can check the mean rather easily by simply counting all the cars: (0*1635 + 1*2800 + 2*2410)/(1635 + 2800 + 2410). This also gives you a hint how to calculate the probabilities.
 
I'm really hoping someone can help me with standard deviation for grouped data. I have read the formula and tried several problems but it just doesn't click.

If I need to calculate a standard deviation of the number of cars in households, what is the correct way to do it?

0 cars - 1635 households
1 car - 2800 households
2 cars - 2410 households

Your help would be much appreciated!
There are several ways to state formulas for SD, so we can't be sure which formula you were given. (tkhunny showed one that is quite likely not familiar to you, for that reason.) Often you will be taught several different formulas that apply in different circumstances, and you could be using the wrong one for this problem.

Please show us the formula you are using, and at least one attempt at using it for this problem, so we can see where the problem is.
 
Top