Standard Deviation

is it A?

My reasoning is...

Range/2 > SD thus, STM1 is SUF

Mean has nothing to do with SD. INSUF

Let me know

iamjakekim wrote:is it A?
Range/2 > SD thus, STM1 is SUF

Can you please tell more abt this rule i.e. how the relation between SD and range exist ? I am not able to find relation between range and standard deviation.

As per my understanding SD is calculated as below:

1. Let's say there are N numbers.
2. Take the mean of numbers.
3. Subtract every number from the mean.
4. Square every number that we received in step 3.
5. Add all the numbers that we get in step 4.
6. Take the average of the number that we get in step 5.
7. Take the positive square root of the number that we get in step 6.
8. standard deviation is the number that we get in step 7 above.

For e.g. let say's numbers are 1, 2, 3. Thus the above steps become:

1. N = 3.
2. Mean = 2.
3. subtracting we get (1, 0, -1)
4. squaring we get (1, 0, 1)
5. Adding = 1 + 0 + 1 = 2.
6. Average = 2/3
7. square root = (2/3)^(1/2)
8. Standard deviation = (2/3)^(1/2)

But in the above calculation looks like there is no relation between range and standard deviation.

Please tell what I am missing here.

Well what we do know is that the range is always greater than the standard deviation. But I don't know how to prove this R>SD*2 formula. Nevertheless, I think you can use it on the GMAT if you don't have any other way to solve the question and want to make a guess and move on.

Can you post the source of this question?

Can some one explain the Range > 2* SD rule..??

i have seen it for the first time...