If you toss 2 dice 10,000 times, how many times would you expect that "the sum of the faces equals 4" happens?
733
550
333
833

Each cube can land in any one of 6 ways.
Two cubes can land in any one of (6 x 6) = 36 ways.

The "successful" outcomes are those for which the sum is 4 .
How many ways can that happen ?

1 . . . 3
3 . . . 1
2 . . . 2

It can happen in 3 ways out of the 36 possible outcomes.
So the probability is

                           3 / 36  =  1 / 12 .

In a large number of rolls, you expect success roughly
once out of every 12 rolls.

In 10,000 rolls, you expect success    (10,000 / 12) = about 833 times.   

A prime number is a number with 2 factors. Since 1 has only 1 factor, it is not prime, because it doesn't have 2 factors.