Question

a number cube labeled 1 though 6 is rolled two times and the sum of the number that end face up is calcalated. what is the probability that the sum of the number is 3?

Answer 1

For sum of two dices to be 3, one of them must be 1 and other must be 2.

Answer 2

When you roll 2 dice, you can get 6 possibilities from the 1st die, and 6 from the 2nd one. Thus, your sample space has 36 (i,e, 6 x 6) possible outcomes.

Now try to list all the way you can get the sum of 3 from two dice. The probability will then be :
\[\frac{\text{number of ways to sum to 3
}}{\text{all 36 outcomes}}\]