Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: integral0 on February 11, 2005, 01:10:11 PM
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A factory manufactures 6 cm long copper tubes with an average mass of 170g. A sample of five such tubes were taken and their masses were found to be 168.13 g. 168.92g, 169.93g, 167.45g, and 170.11g respectively. The standard deviation for the masses of this sample is approximately.
a. 1.67
b. 0.835
c. 0.691
d. 0.668
e. 1.14
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In order to do this problem, you must use the formula for standard deviation http://mathworld.wolfram.com/StandardDeviation.html
I'm pretty sure I'm using the formulae correctly; however, I wind up with 1.67 as the standard deviation
while the answer is 1.14
What am I doing wrong? (the work is too extensive so I didn't write it out and I don't expect someone to either when solving it...I just want to know if you guys get 1.67 too or if you are getting 1.14... and maybe, you'll show me how =)
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your mean is 170
1. find the mean absolute deviation between the measurements and the mean
2. the average of thise values should give you 1.136 or 1.14
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actually...i solved it a couple of days ago...and the mean is not 170 g . . .that's the big mistake...that's the population mean...that's not the sample mean.... if you find the sample mean...than you will get 1.14g