What's the probability of rolling 2 ordinary (fair) 6 sided dice to get the total 7?

First, certain types of events in probability are called independent. And, when there is a situation with a pair of independent events, a multiplication rule is applied. This rule specifically looks at the probability that both of the independent events occur.

A standard die has six sides with numbers 1, 2, 3, 4, 5 and 6. If the die is fair, then all of the outcomes are equally likely. Since there are six possible outcomes, the probability of obtaining any side of the die is 1/6.

When rolling two fair dice, it more than doubles the difficulty of calculating probabilities. This is because rolling one die is independent of rolling a second one. One roll has no effect on the other one. So, to deal with the independent events, the multiplication rule is used. It demonstrates that by rolling 2 dice really 1 of 36 (6 x 6) outcomes are possible.

So, when 2 dice are thrown simultaneously and the sum total is 7, seven as the possible outcome is one of six (1/6 or 17%).