PROBABILITY! Let’s learn about probability and chance!

What is probability? Probability is the measure of how likely an event or outcome is. Different events have different probabilities!

How do we describe probability? You can describe the probability of an event with the following terms: –certain (the event is definitely going to happen) –likely (the event will probably happen, but not definitely) –unlikely (the event will probably not happen, but it might) –impossible (the event is definitely not going to happen) Can you think of examples of each type of event?

How do we express probabilities? Usually, we express probabilities as fractions. –The numerator is the number of ways the event can occur. –The denominator is the number of possible events that could occur. Let’s look at an example!

What is the probability the spinner will land on the number 3?

Ask yourself the following questions: 1. How many 3’s are on the spinner? 2. How many possible numbers could the spinner land on?

What is the probability the die will land on an even number? Remember, a die has six sides. Numbers 1, 2, 3, 4, 5, and 6 are each depicted once on the die.

Ask yourself the following questions: 1. How many even numbers are on the die? 2. How many possible numbers could the die land on? 3 6

What is the probability that I will choose a red marble? In this bag of marbles, there are: –3 red marbles –2 white marbles –1 purple marble –4 green marbles

Ask yourself the following questions: 1. How many red marbles are in the bag? 2. How many marbles are in the bag IN ALL? 3 10

Now that we are familiar with probability, we will talk about the two different types of probability!

Experimental vs.Theoretical Experimental probability: P(event) = number of times event occurs total number of trials Theoretical probability: P(E) = number of favorable outcomes total number of possible outcomes

How can you tell which is experimental and which is theoretical probability? Experimental: You tossed a coin 10 times and recorded a head 3 times, a tail 7 times P(head)= 3/10 P(tail) = 7/10 Theoretical: Toss a coin and getting a head or a tail is 1/2. P(head) = 1/2 P(tail) = 1/2

Experimental probability Experimental probability is found by repeating an experiment and observing the outcomes. P(head)= 3/10 A head shows up 3 times out of 10 trials, P(tail) = 7/10 A tail shows up 7 times out of 10 trials

Theoretical probability P(head) = 1/2 P(tail) = 1/2 Since there are only two outcomes, you have 50/50 chance to get a head or a tail. HEADS TAILS

Compare experimental and theoretical probability Both probabilities are ratios that compare the number of favorable outcomes to the total number of possible outcomes P(head)= 3/10 P(tail) = 7/10 P(head) = 1/2 P(tail) = 1/2