Look at the first 6 positive integers:
1, 2, 3, 4, 5, 6.
Which ones are even?:
2, 4, 6
That's 3 out of 6, so out of the first 6, P(even) = 3/6 = 1/2
Which ones are odd?:
1. 3, 5,
That's 3 out of 6, so out of the first 6, P(odd) = 3/6 = 1/2
Which one is even when divisible by 3?
6,
That's 1 out of 6, so out of the first 6, P(even when divisible by 3 = 1/6
Now realize that we can say the same thing about the next set of
6 positive integers:
13, 14, 15, 16, 17, 18
3 out of those 6 are even, 3 out of those 6 are odd, and 1
out of those 6 is even when divisible by 3 (just 18).
It's the same with next 6, and the next 6, etc., etc.
So for the set of ALL positive integers,
P(even)=1/2, P(odd) = 1/2, P(even when divisible by 3) = 1/6
Edwin