When applying a combination of spreads (e.g. peanut butter and apricot jam) on freshly toasted bread, the number of knives required can be deduced using the following formula:-
n + 1
(where n = the number of different spreads)
This gives you one knife to retrieve the desired amount of each spread from its container, and an extra one to apply it on the piece of toast evenly without contaminating the unused portions of spread.
