P(E) + P(not E) = 1

P(E) + P(not E) = 1

This is because the probability of any event in the sample space must equal 1. Therefore if we know the probability of E we can also find the probability of not E.


Thus if we want to know the probability of not rolling a 2 on an even die we can say

P(rolling a 2) = 1/6

1/6 + P(not rolling a 2) = 1

P(not rolling a 2) = 1 - (1/6) = (5/6)