Final answer:
Harris ate 12/k - 1 slices of pizza after a 12-slice pizza was divided evenly among k friends and he ate one less than he was given.
Step-by-step explanation:
To find out how many slices of pizza Harris ate, we initially need to determine how many slices each person would get if the 12-slice pizza is divided evenly among k friends.
Each friend would get 12/k slices.
Since Harris ate 1 fewer slice than he was given, we subtract 1 from the number of slices he was supposed to get.
Therefore, the expression for the number of slices Harris ate is 12/k - 1.