sample mean, variance and SD

This is to all R-helpers (Sarah is just the one that I am replying to),

Have we become a little too draconian on the "not a homework help list"
issue?
...

As usual, a thoughtful comment on a problem that does not have a 
straightforward solution. The actual responses to obvious homework 
questions range from curt refusals to worked examples. I don't know the 
official status of the "no homework" policy if there is one.

My responses are guided by their expected utility. If the question 
appears to be asked by someone who has just gotten stuck on an esoteric 
quirk of R (and the extraction operators are a good example), I'll try 
to get them over the hump. In this particular case, parvez_200207 seems 
to have answered the question and not realized it. Maybe this was due to 
something that parvez_200207 didn't even know was going on (e.g. a 
sink() was operating) or maybe it was just complete cluelessness. If I 
strongly suspected the former, I probably would have answered.

Jim