Sum of the
points ot the two rolls
Roll 1
1 2 3
4 5 6
Roll 2
1
2 3 4
5 6 7
2
3 4 5 6 7
8
3
4 5
6 7 8 9
4
5 6 7 8 9
10
5
6 7
8 9
10 11
6
7 8 9 10 11
12
Prime results:
2: once, 1
3: twice, 2
5: four times, 4
7: six times, 6
11: twice, 2
The easiest
way is to count all the results in which none of the rolls was a three and the
sum of the two rolls was not a prime number: it is 14 results.
Now subtract
those 14 results from the 36 possible outcomes, the difference is the number of
results in which either the sum of the rolls is a prime or at least one of the
numbers is three: 36 – 14 = 22
Probability
= positive events / total events
Probability:
22/36 = 11/18
Please, let me know if my explanation was clear enough.
