# Math Help - Multiplication and Addition rules

1. ## Multiplication and Addition rules

Well I want to ask what is the difference between Multiplication and Addition rules and when to use them to find out the probabilities of events' occurence. For example: When you toss two coins what's the probability that they are heads up?
Thank you for helping me.

2. Originally Posted by fromia
Well I want to ask what is the difference between Multiplication and Addition rules and when to use them to find out the probabilities of events' occurence. For example: When you toss two coins what's the probability that they are heads up?
Thank you for helping me.
You use multiplication when the two events are independent of one another. In the case of flipping coins, the probability that a coin is heads-up is 1/2. So the probability of flipping two coins heads-up is (1/2)(1/2) = 1/4. You add distinct probabilities when you want to find the probability of an event that encompasses several probabilities, such as: What is the probability of drawing an 8 or a 9 from a standard deck of 52 cards? It is the same as the probability of drawing an 8 plus the probability of drawing a 9.