Let me repeat your problem to see whether I understand.
You have 16000 row (and each of them contains numbers text etc )
You want to randomly choose 400 rows out of given 16000.
If I am right then you should use function OFFSET and RAND together.
Let in column A (A1:A16000) are 16000 numbers
Let in column B (B1:B400) are formulas =FLOOR(RAND()*16000,1)
And let the column C (C1:C400) is filled by formulas =OFFSET($A$1,B1,0) (B1
for row 1 -> B2 for row 2 -> B3 for row 3 etc)
After each F9 column C is different random sample (uniformly distributed)
from A.
I think that this number example could be easily transformed into your
problem with rows.
rd
PS: later on you can change B column to =FLOOR(RAND()*(16000-1)+1,1), which
is more appropriate formula for you.