# Homework Help: Statistics Question - Find Standard Deviation of 5 numbers but only 4 given.

1. Jan 30, 2013

### JiHbE

For a sample of size 5, if x1 - x̄ = -5, x2 - x̄ = 9, x3 - x̄ = -7, and x4 - x̄ = -2, then the sample standard deviation is:
a. 5.639
b. 6.782
c. None of the other answers are correct
d. 6.305
e. 6.066

Please note that x̄ is x-bar (mean of sample).

This question has been puzzling me. At first I thought there was an error because only 4 numbers are listed but it says there sample size is 5. But, this is a valid question.

So, I'm going to need the x5- x̄ value in order to calculate the standard deviation.
This is where I'm lost.... could someone please provide some assistance?

Thank you so much for your time.

2. Jan 30, 2013

### Staff: Mentor

Can you express the mean in terms of x1 to x5? Rewriting that equation a bit will give you x5 - xmean.

3. Jan 30, 2013

### SammyS

Staff Emeritus
Hello JiHbE. Welcome to PF !

What is $\ \ x_1+x_2+x_3+x_4+x_5-5\cdot\bar{x}\ ?$

4. Jan 30, 2013

### JiHbE

Can you tell me how you typed x-bar? :)

What I do know is that:

mean = (x1 + x2 + x3+ x4 + x5)/5

Therefore,

5mean = (x1 + x2 + x3 + x4 + x5)

5. Jan 30, 2013

### Staff: Mentor

You can see the code via the "quote" button in his post.

Right. Now you can use your knowledge about $x_1-\bar{x}$ and so on.