This comes from this website: https://web.stanford.edu/~guertin/risk.notes.html

Its about calculating probabilities of the game Risk.

The

probability of throwing N as the “highest” dice with two dice must be the

probability of throwing “N or less” MINUS the probability of throwing

“N-1 or less” with two dice.

i don’t understand why its P(“N or less”) – P(“N-1 or less” with 2 dice).

Is there a law of probability that can explain this?