# Homework Help: Statistics - finding the mean

1. Jan 17, 2009

### Fairy111

1. The problem statement, all variables and given/known data

From the data:
x=-5 -4 -3 -2 -1 0 1 2 3 4 5
y= 1 5 4 7 10 8 9 13 14 13 18

These values are in a table, ie -5 corresponds to 1, -4 to 5 and so on.
I have to find:
Sxx=Sum of [x(i) - mean of x]^2

Sxy=Sum of [x(i) - mean of x][y(i) - mean of y]

Im not sure how to do this. Whats the mean of x?

2. Relevant equations

3. The attempt at a solution

2. Jan 17, 2009

### HallsofIvy

The mean is just the arithmetic average of the numbers. In this case, since there are 11 values for each of x and y, add the numbers and divide by 11.

3. Jan 17, 2009

### Fairy111

x is not a variable, the numbers are just -5, -4, -3 ...3,4,5
so when you add them up you'l just get zero.
This is what is confusing me.

4. Jan 17, 2009

### HallsofIvy

If x is -5, 4, ..., 4, 5, then it's pretty darn variable! What do you think "variable" means?

Is said before that the mean is the average: sum divided by 11. What is 0/11? Why is that confusing?

It is true here that you x values form an arithmetic sequence with an odd number of values: and the mean of such a sequence is the middle value.

5. Jan 17, 2009

### microguy

Did you mean Mean or Median?

6. Jan 17, 2009

### future_phd

In this situation the mean and the median are the same.