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hi
can anybody help me
a) what does standard deviation describe about a set of data?
b)Table below shows the crushing strengths of concrete samples, determine
1) Mode, mean and median and standard deviation
2) standard deviation likely for the population
261, 245, 385, 253, 298, 284, 320, 335, 297, 335
300, 314, 345, 310, 279, 298, 305, 298, 320, 300
thanks
well i worked out the mean to be 289.6 by adding all the numbers then dividing by how many they are Ex/n (sum of x divided by the number of terms) im doing this to for my S1 exam i hate stats
i think to do standard deviation you square all the numbers then add them up then divide by the number of terms then subract the mean squared
(289.6)^2 then square root the answer i'll work it out in a bit
If you just want the answer, Excel has a STDEV function that takes a range of cells and calculates it like
=STDEV(A1..A25)
However, you should really read up on statistics, as this sounds like basic statistics homework.
Bill
For the population (point 2)), you use the function =STDEVP(A1..A#).
Rui
standard deviation:
http://www.mathsrevision.net/gcse/sdeviation2.gif
where x bar is average
basicly u take the first piece of data, subtract the average, square the result
then u repeat this for your second piece of data, third, and so on, once you do this for all of your data you take the sum of these results and divide by the number of data pieces. square root and you are done