Hi mikerickson!!

Good things:
thanks so much for your answer, you're a master!!


Bad things:
I made a mistake in my first message... what I need is that if my community is:

species A --> 13 insects
species B --> 53 insects
species C --> 20 insects

TOT number of insects in the community: 86

my 1000 random sample have to take randomly 50 insects from this pool, so that I can't take 35 insects from species A because I only have 13 of these (that's my mistake in the previous msg )). In this way, each species is constrained by ITS number (13 for A, 53 for B and 20 for C), and the total sample size has to be 50. Example:

species A --> 5 insects
species B --> 34 insects
species C --> 11 insects

TOT number of insects in the random sample: 50

Hoping this is not a big problem for Excel....

sorry for my previous msg!!

Daniele