Find the probability of rolling a number bigger than 4 and subtract that by 100%;
P(5)= 1/6 <-- 6 possible outcomes, 1, 2, 3, 4, 5 or 6
P(6)= 1/6
You could have rolled a 5 or 6. When the word or is used, the probabilities are added together, when and is used, they are multiplied.
(1/6)+(1/6)=2/6
1-P(5)+P(6)
=1-(2/6)
=(6/6)-(2/6)
=4/6
Therefore the probability of not rolling a number larger than 4 is 4/6 or 2/3.
Hope I helped :)