Addition Rule and when do you use the Multiplication Rule in probablity , What is the difference?

Question

Im currently trying to understand addition and multiplication probability I just need some assistance for a clearer understanding

Answer 1

A major factor is if the question is asking OR, or if it is asking AND.

 

Let's take for example rolling a six-sided die:

What is the probability that the die will roll a 3 OR a 6?

The die has six sides, and we are asking to see if it lands on 2 of those six sides (that is, have two chances to roll on a side asked for):

1/6 + 1/6 = 2/6, or 1/3 simplified

 

What is the probability of the die rolling a 3 AND then a 6?

The first hurdle to cross is to roll that 3, a one in six chance.

Once we pass that, there is a new, second hurdle to clear--rolling a 6, another one in six chance.

1/6 * 1/6 = 1/36

 

I hope this gives you an idea of when each one is applied.