try something like
for your exAMPLE in C1 enter
if(countif($B$1:$B$3,A1)0,A1)
and copy down to C3

"HERNAN" wrote:

I have 2 columns with numbers Column A and B.
I need to COPY on column "C" the ones that are duplicates.
That's it.
(I don't need to find them using conditional formating, I need to copy them)
Please Im gettin crazy with this. THANK YOU IN ADVANCE!!!!

A B
10 30
15 50
20 15