You need more data to find the standard deviation, but the mean attendance would be 50 - .1(50).
I searched Google under the key words "standard deviation" to get these possible sources:
http://en.wikipedia.org/wiki/Standard_deviation
http://www.robertniles.com/stats/stdev.shtml
http://davidmlane.com/hyperstat/A16252.html
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
I hope this helps. Thanks for asking.
A club has 50 members. If there is a 10% absentee rate per meeting, find mean and standard deviation: How do you do the problem step by step
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