Calculating Standard Deviation Homework

[EdmureTully]

Homework Statement

I have to calculate the standard deviation

Homework Equations

http://0.tqn.com/d/statistics/1/0/M/-/-/-/standarddev.GIF

The Attempt at a Solution

0.64 0.4096
2.06 4.2436
0.16 0.0256
3.24 10.4976
1.74 3.0276
1.06 1.1236
4.04 16.3216
1.56 2.4336
1.3 1.69
3.64 13.2496
3.16 9.9856
3.04 9.2416
0.86 0.7396
3.56 12.6736
2.94 8.6436
1.74 3.0276
2.96 8.7616
2.34 5.4756
6.46 41.7316
2.76 7.6176

total = 151.9204

uncorrected sd = 2.75
corrected sd = 2.83

1 89.20
2 86.50 2.70
3 88.40 1.90
4 91.80 3.40
5 90.30 1.50
6 87.50 2.80
7 92.60 5.10
8 87.00 5.60
9 89.80 2.80
10 92.20 2.40
11 85.40 6.80
12 91.60 6.20
13 87.70 3.90
14 85.00 2.70
15 91.50 6.50
16 90.30 1.20
17 85.60 4.70
18 90.90 5.30
19 82.10 8.80
20 85.80 3.70

the answer they get is 2.91

average is 88.56

did i make any calculation error?

I can't believe i made any calculation error

 

[vela]

Yes, you made some errors. Your value for the mean is correct. One of your differences is off, and you compounded that error by not summing the squares accurately.

It would have helped if you described what you were doing instead of just posting arrays of unlabeled numbers and leaving it to others to decipher what you did.

 

[EdmureTully]

Ok, thanks. One last thing, do I have to divide by n-1 or just n?

 

[vela]

For an unbiased estimator, you need to divide by n-1.

 

[Ray Vickson]

Homework Statement

I have to calculate the standard deviation

Homework Equations

http://0.tqn.com/d/statistics/1/0/M/-/-/-/standarddev.GIF

The Attempt at a Solution

0.64 0.4096
2.06 4.2436
0.16 0.0256
3.24 10.4976
1.74 3.0276
1.06 1.1236
4.04 16.3216
1.56 2.4336
1.3 1.69
3.64 13.2496
3.16 9.9856
3.04 9.2416
0.86 0.7396
3.56 12.6736
2.94 8.6436
1.74 3.0276
2.96 8.7616
2.34 5.4756
6.46 41.7316
2.76 7.6176

total = 151.9204

uncorrected sd = 2.75
corrected sd = 2.83

1 89.20
2 86.50 2.70
3 88.40 1.90
4 91.80 3.40
5 90.30 1.50
6 87.50 2.80
7 92.60 5.10
8 87.00 5.60
9 89.80 2.80
10 92.20 2.40
11 85.40 6.80
12 91.60 6.20
13 87.70 3.90
14 85.00 2.70
15 91.50 6.50
16 90.30 1.20
17 85.60 4.70
18 90.90 5.30
19 82.10 8.80
20 85.80 3.70

the answer they get is 2.91

average is 88.56

did i make any calculation error?

I can't believe i made any calculation error

What on Earth is your data? Is the first data set a list of 40 numbers (presented as two lists of 20, or is it two separate lists, each of size 20? If it is a single list of size 40 I get a total of 210.1804; if it is two lists of size 20 each I get a total of 49.26 for the first list and a total of 160.92094 for the second list. None of these match what you claim---but your analysis is totally meaningless because you do not give any clues as to what you are doing.