You roll a standard number cube. find p (number is not 3)

I suppose you mean P is the probability of getting a number that is not 3.

Standard number cubes usually contain numbers 1 through 6. The question wants us to take out the number 3 from the possible numbers and find the probability that the number is not 3.

We start off with 6 numbers (1,2,3,4,5,6). Since we take out the number 3, that leaves us with 5 numbers. The cube has not changed its contained numbers so we know the maximum amount of numbers we can end up with is 6.

Therefore, the probability of rolling a number that is not 3 is 5/6.

P (x≠3) = 5/6

you can get six numbers form a cube. but you don't need 3, so you need 5 numbers. that's it.