How to put 9 pigs into 4 pens so that there are an odd number of pigs in each pen? So I'm tutoring at the library and an elementary or pre K student shows me a sheet with one problem on it:

Put 9 pigs into 4 pens so that there are an odd number of pigs in each pen.

I tried to solve it and failed! Does anybody know how to solve this? This question seems ridiculously difficult and impossible IMO.
Since this has been exposed, some claim, to be a riddle and not a bona fide math question, why not completely drive the stake through its heart:

Pen 1: 7 pigs

Pen 2: 1 pig

Pen 3: 3 pigs

Pen 4: -2 pigs

Now the astute reader will note that -2 pigs is a pretty darn odd number of pigs to be in a pen!
I assume in elementary school they are not expected to know the parity of zero, so why not this:

3,3,3,0

Thats 9, and all "not even" (again, forget about the parity of zero).