Question

Standard deviation question, please help!

Answer 1

@kropot72

Answer 2

The first step is to add the 7 amounts and divide the total by 7 to find the mean amount.
Can you do that and post the result?

Answer 3

$5.10

Answer 4

Correct. Next you need to subtract the mean from each of the 7 daily amounts and square the result. Here is the calculation for Sunday as an example:
\[4.85-5.10=-0.25\]
\[(-0.25)^{2}=0.0625\]
Can you do that for each of the remaining 6 days and post the results?

Answer 5

0, 0.16, 0.5625, 0.36, 0.01, 0.81

Answer 6

All correct except for the Wednesday calculation. Please check.

Answer 7

.1225

Answer 8

Correct! Now add the 7 results and divide the total by 7. Then take the square root of the result to get the standard deviation.

Answer 9

I got .0474617347, right?

Answer 10

Not really. What did you get for the sum of the following:
0.0626 + 0 + 0.16 + 0.1225 + 0.36 + 0.01 + 0.81= ?

Answer 11

1.525

Answer 12

Then what is \[1.525\div 7=?\]

Answer 13

.2178571429

Answer 14

And the square root of that?

Answer 15

Ohh, I tried squaring it last time, I got .466751693

Answer 16

Good work! So rounding, it would be 0.46675

Answer 17

Sweet, so that is my answer for part a?

Answer 18

Or I guess rounded to the thousanth 0.467

Answer 19

That is the answer for part a. You are correct in rounding to the nearest thousanth, I forgot that the question specified that.

Answer 20

Awesome, could you give me a hand on part b now? :P

Answer 21

Certainly I can help with part b. Have you any idea what would happen to the value of the standard deviation if the sample size n increased and the sum of the squared differences remained the same?

Answer 22

No, no idea, sorry I'm really bad at statistics

Answer 23

Well, the calculated standard deviation would reduce. This could indicate that the original sample size was too small.

Answer 24

hmmm, ok, I think that makes sense, and the second part of the question? What does that mean in real life?

Answer 25

Be suspicious of results calculated from small samples. The level of uncertaity can be high.

Answer 26

Thanks, I really really appreciate your help, I would give you 10 medals if I could. :)

Answer 27

You're welcome :)