A cow-culator! (Cue groans)
Second Caribou: Owlgebra.
Three. One to get the punchline, and one to point out the math is wrong.
You use a cow-culator. Or you round them up. Or any other method the commenters want.
They use a cow-culator! Ba-dum-tsss!
A bull.
Barns and no-bulls. (This joke was made up by my 7 year-old cousin.)