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PROBABILITY

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Definitions An experiment is a situation involving chance or probability that leads to results called outcomes An outcome is the result of a single trial of an experiment An event is one or more outcomes of an experiment Probability is the measure of how likely an event is

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**Examples of Definitions:**

A spinner has 4 equal sections colored yellow, blue, green, and red. What are the chances of landing on blue? The experiment is spinning the spinner The possible outcomes are landing on yellow, blue, red, or green One event of this experiment is landing on blue The probability of landing on blue is one-fourth

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More on Probability Probability is a number from 0 to 1 that tells you how likely something is to happen. Probability can be either theoretical or experimental.

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**Probability THEORETICAL**

Theoretical probability can be found without doing an experiment. When each event is equally likely to happen. EXPERIMENTAL Experimental probability is found by repeating an experiment and observing the outcomes.

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**Theoretical Probability**

The probability of an event (A) is the number of ways event (A) can occur divided by the total number of possible outcomes. P(A) = The number of outcomes where A can occur The total number of possible outcomes So, using the spinner experiment, what is the probability of landing on blue? P(blue) = 1 4

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**THEORETICAL PROBABILITY**

I have a quarter My quarter has a heads side and a tails side Since my quarter has only 2 sides, there are only 2 possible outcomes when I flip it. It will either land on heads, or tails HEADS TAILS

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**THEORETICAL PROBABILITY**

When I flip my coin, the probability that my coin will land on heads is 1 in 2 What is the probability that my coin will land on tails?? HEADS TAILS

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**Theoretical Probability**

Right!!! There is a 1 in 2 probability that my coin will land on tails!!! HEADS TAILS A probability of 1 in 2 can be written in three ways: As a fraction: ½ As a decimal: .50 As a percent: 50%

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**Theoretical probability**

When I spin this spinner, I have a 1 in 4 chance of landing on the section with the red A in it. A

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**A 1 in 4 chance can be written 3 ways:**

Theoretical Probability A 1 in 4 chance can be written 3 ways: As a fraction: ¼ As a decimal: .25 As a percent: 25% A The probability is equally likely when each section is the same size

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**Theoretical Probability**

I have three marbles in a bag. 1 marble is red 1 marble is blue 1 marble is green I am going to take 1 marble from the bag. What is the probability that I will pick out a red marble?

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**Theoretical Probability**

Since there are three marbles and only one is red, I have a 1 in 3 chance of picking out a red marble. I can write this in three ways: As a fraction: 1/3 As a decimal: .33 As a percent: 33%

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**Experimental Probability**

Experimental probability is found by repeating an experiment and observing the outcomes.

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**Experimental Probability**

The probability based on the outcomes you obtained in an experiment. P(A) = Number of times event A occurs in the experiment Total number of trials

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**Experimental Probability**

In our spinner experiment, if we spin 10 times and the outcomes were: Blue 4 Red 3 Green 2 Yellow 1 P(blue) = 4 or 2

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**Experimental Probability**

Remember the bag of marbles? The bag has only 1 red, 1 green, and 1 blue marble in it. There are a total of 3 marbles in the bag. Theoretical Probability says there is a 1 in 3 chance of selecting a red, a green or a blue marble.

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**Experimental Probability**

Draw 1 marble from the bag. It is a red marble. Record the outcome on the tally sheet

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**Experimental Probability**

Put the red marble back in the bag and draw again. This time your drew a green marble. Record this outcome on the tally sheet.

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**Experimental Probability**

Place the green marble back in the bag. Continue drawing marbles and recording outcomes until you have drawn 6 times. (remember to place each marble back in the bag before drawing again.)

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**Experimental Probability**

After 6 draws your chart will look similar to this. Look at the red column. Of our 6 draws, we selected a red marble 2 times.

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**Experimental Probability**

The experimental probability of drawing a red marble was 2 in 6. This can be expressed as a fraction: 2/6 or 1/ a decimal : or a percentage: 33%

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**Experimental Probability**

Notice the Experimental Probability of drawing a red, blue or green marble.

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**Comparing Experimental and Theoretical Probability**

Look at the chart at the right. Is the experimental probability always the same as the theoretical probability?

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**Comparing Experimental and Theoretical Probability**

In this experiment, the experimental and theoretical probabilities of selecting a red marble are equal.

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**Comparing Experimental and Theoretical Probability**

The experimental probability of selecting a blue marble is less than the theoretical probability. The experimental probability of selecting a green marble is greater than the theoretical probability.

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**Probability Review There are 2 types of probability:**

Probability is a number from 0 to 1 that tells you how likely something is to happen. There are 2 types of probability: Theoretical (can be found without doing an experiment) Experimental (can be found by repeating an experiment and recording outcomes.)

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Probability Review Probability can be expressed as a fraction, a decimal or a percentage.

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Probability Chances Are… You can do it! Activity #1

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**What is the probability of rolling an even numbered sum?**

1,1 1,2 2,1 1,3 3,1 2,2 2,3 3,2 1,4 4,1 2,4 4,2 1,5 5,1 3,3 3,4 4,3 2,5 5,2 1,6 6,1 2,6 6,2 3,5 5,3 4,4 3,6 6,3 4,5 5,4 4,6 6,4 5,5 5,6 6,5 6,6 What is the probability of rolling an even numbered sum? A sum smaller than 4? A square number sum?

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**What is the probability of rolling an even number sum?**

A number sum smaller than 4? A square number sum? 18 out of 36 3 / 36 8 / 36 Write like a mathematician in your journal, showing these questions and answers. Click mouse to see answers

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**What is the probability of rolling an even number sum? **

P (even number sum) = 18/36 or 1/2 A number sum smaller than 4? P (number sum smaller than 4) = /36 or 1/12 A square number sum? P (square number sum)= 8/36 or 4/9 End of Activity

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Probability Chances Are… You can do it! Activity #3

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DRAWING MARBLES A jar contains two red marbles, three blue marbles, and four green marbles. Niki draws one marble from the jar, and then Tom draws a marble from those remaining. What is the probability that Niki draws a green marble AND Tom draws a blue marble? Express your answer as a common fraction.

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**# of desired outcomes # of total possible outcomes REMEMBER... SO...**

Niki has a 4/9 chance of drawing a green and Tom has a 3/8 chance of drawing a blue.

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**# of desired outcomes # of total possible outcomes REMEMBER... SO...**

Niki has a 4/9 chance of drawing a green and Tom has a 3/8 chance of drawing a blue.

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4/9 x 3/8 = 12/72 or 1/6 There is a 1/6 chance that Niki will draw a green marble AND Tom will draw a blue marble End of Activity So...

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