Answer:
If the first slice is pepperoni, then we have left:
1 slice of pepperoni.
2 slices of mushrooms.
2 slices of anchovy.
Then the possible combinations are:
Pepperoni and pepperoni (in only one combination)
Pepperoni and mushrooms (in two combinations, because there are two slices left)
Pepperoni and anchovy (Again in two combinations, because there are two slices left)
These are the 3 possible combinations, 5 in total.
