When calculating probability, we are comparing the number of favorable outcomes to the number of possible outcomes. To calculate the probability of rolling two numbers which sum is less than 9 we will use the Probability Formula.
P=Favorable Outcomes/Possible Outcomes
First, let's calculate the number of possible outcomes. We will do this by using Fundamental Counting Principle. When tossing a number cube there are 6 possible outcomes. When throwing two cubes we multiply numbers of possible outcomes.
6 * 6 = 36
To find the number of favorable outcomes we will begin by making a table of possible outcomes. In the columns and rows we have possible outcomes of each cube roll.
1
2
3
4
5
6
1
1, 1
2, 1
3, 1
4, 1
5, 1
6, 1
2
1, 2
2, 2
3, 2
4, 2
5, 2
6, 2
3
1, 3
2, 3
3, 3
4, 3
5, 3
6, 3
4
1, 4
2, 4
3, 4
4, 4
5, 4
6, 4
5
1, 5
2, 5
3, 5
4, 5
5, 5
6, 5
6
1, 6
2, 6
3, 6
4, 6
5, 6
6, 6
Notice that there are 26 favorable outcomes. Therefore, the probability of rolling two numbers which sum is less than 9 is 2636.
