Well, if you multiply 16 oz (1 lbs) by (1/3).
You get 5.28 oz for 3 slices.
If you divide 5.28 by 3, you get 1.76 oz per slices.
This means that he can eat 2 full slices of turkey and half a slice in order to eat less than (1/4) of a pound.
So the answer would be 2-2.5 slices.