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Grade 9:  The Learning Equation Math

42.03 Independent Events

4icon.gif (5323 bytes)

Chance and Uncertainty

Refresher pp 112-13

 

 

SeekAWord2ech.class Author

Prerequisite Skills:

 

 

Learning Outcomes:

The student will: 

Independent Event an event whose outcome does not affect the occurrence of another event

EnrichmentSample calculations

  • draw two cards at random from a standard deck with replacement
  • draw two marbles at random from a bag with replacement
  • draw two candies at random from a dish with replacement
  • draw two numbers at random from a hat with replacement
  • select two keys at random from a keyring with replacement
  • select two tools at random from a toolbox without replacement
  • roll two dice
  • spin two spinners
  • flip two coins
Dependent Event an event whose outcome affects the occurrence of another event.
  • draw two cards at random from a standard deck without replacement
  • draw two marbles at random from a bag without replacement
  • draw two candies at random from a dish without replacement
  • draw two numbers at random from a hat without replacement
  • select two keys at random from a keyring without replacement
  • select two tools at random from a toolbox without replacement

Independent and Dependent Events - many examples

GCSE Answers' Tutorial on Probability - many examples

Tables/Tree Diagrams

 

 

Two Six-sided Dice

A tree diagram or table shows the possibilities.  The traditional tree diagram is incorporated into the following chart.  A tree diagram will include the possibilities and the branches, while the chart illustrates the same possibilities without the branches.  

Method 1:  Tree Diagram

Roll Die 1 until you get 1, then look at the charts between the two dice.  Roll Die 2.  It will display the value from 1 to 6.   Each possibility for Die 1 connects with the six possibilities for Die 2.  There are 36 possibile outcomes when you roll two dice.

Event A:  Die Toss

1tree.png (27212 bytes)

1
2
3
4
5
6

2tree.png (27212 bytes)

1
2
3
4
5
6

3tree.png (27212 bytes)

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2
3
4
5
6

4tree.png (27212 bytes)

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5tree.png (27212 bytes)

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6tree.png (27212 bytes)

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2
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6

Event B:  Die Toss

 

Method 2:  Table

The virtual spreadsheet below has been started for you.  Complete the spreadsheet to show the 36 possibilities for 2 six-sided dice thrown.  Click on the Check button to confirm your solution.

correct.gif (1227 bytes)

source:  Robert's Online Spreadsheet!   Disclaimer

 

Did You See the Pattern?

 

Possibilities for the sum of two dice

1 2 3 4 5 6 7 8 9 10 11 12
The number of times each event occurs on the the tree diagram or table. 0 1 2 3 4 5 6 5 4 3 2 1
Total possible outcomes 36 3636 36 36 36 36 36 36 36 36 36 36
Theoretical probability for each sum 0/36 1/36 2/36 3/36 4/36 5/36 6/36 5/36 4/36 3/36 2/36 1/36

 

 

Two Coins

Event A:  Coin 1 Flip

Event B:  Coin 2 Flip

 

Method 1:  Tree Diagram

There are 4 possible outcomes when you flip two coins.  The table below shows the same possibilities, but does not include the branches connecting each possibility for Coin 1 with the two possibilities for Coin 2.

Coin 1 Coin 2
H H
T
T H
T

Method 2:  Table

Make a chart to show the 4 possibilities for 2 coins.  Click on the Check button to confirm your solution?

correct.gif (1227 bytes)

 

 

A Coin and Six-sided Die

Event A:  Coin Flip

Event B:  Die Toss

 

Method 1

Complete the tree diagram to show all of the possible outcomes of flipping a coin and tossing a die.  Compare it to the table below.   It should show the same possiblilities, but will include branches connecting each possibility for Die with the two possibilities for Coin. There are 12 possible outcomes when you roll a die and flip a coin.

Die Coin
1 H
T
2 H
T
3 H
T
4 H
T
5 H
T
6 H
T

Method 2

Make a chart to show the 12 possibilities for a coin and  six-sided die tossed.  Click on the Check button to confirm your solution.

correct.gif (1227 bytes)

 

A 5 Sector Spinner and Coin

Event A:  Spin Wheel

Event B:   Coin Flip

 

Complete the tree diagram to show all of the possible outcomes of flipping a coin and spinning a 5 sector spinner.  Compare it to the table below.  It should show the same possiblilities, but will include branches connecting each possibility for Spinner with the two possibilities for Coin. There are 10 possible outcomes when you spin a 5 sector spinner and flip a coin.

Spinner Coin
green H
T
blue H
T
white H
T
grey H
T
red H
T

number of possible outcomes = 5 x 2 = 10

Remember when there are two independent events, the number of possible outcomes equals the number of possible outcomes of the first event times the possible outcomes of the second event.

 

Coin and 4 Sector Spinner

Make a chart to show the 8 possibilities for a coin and four sector spinner (blue, green, cyan, magenta)?    Click on the Check button to confirm your solution.

correct.gif (1227 bytes)

 

Theoretical Probability Practice

To be independent, one result cannot effect the probability of the other.

 

Lesson on Probability of Independent Events

Rolling Dice Probability (Equally Likely Events)

Experimental probability is:
# times the event occurred
total outcomes
Theoretical probability is:
# ways the event can occur
total possible outcomes

 

  1. Create a table like the one on the right.
  2. Click on "Roll Dice" 36 times and record the results in the Experimental column.
  3. Compare the experimental and theoretical probability.

 
Sum of Dice Experimental Results Theoretical Probability
1 0 0
2 /36 1/36
3 /36 2/36
4 /36 3/36
5 /36 4/36
6 /36 5/36
7 /36 6/36
8 /36 5/36
9 /36 4/36
10 /36 3/36
11 /36 2/36
12 /36 1/36
Total 36 36

Additonal resource:  Probability:   What are Your Chances?

 

Probability of Rolling Die and Spinning a Colour

Event A:  Toss Die

Event B:  Spin Wheel

 

Toss one six-sided dice and spin a five sector color spinner.   What is the theoretical probability of a particular number and color being selected?

Solution:

You can use a real die and spinner or use the virtual ones above.  The probability of of any number being tossed is 1/6, while the probability of the spinner stopping on each color is 1/5.  Refer to the probability of the sum of two dice tossed if necessary.    Examples:

P(5, green) means the probability of tossing 5 and spinning green

P(3, red) means the probability of tossing 3 and spinning red

Complete 30 trials and complete the experimental probability.

Two Events Experimental Probability Theoretical Probability
P(5, green) = /30 1/6 x 1/5 = 1/30 = 0.0333... = 3.3%
P(3, blue) = /30 1/6 x 1/5 = 1/30 = 0.0333... = 3.3%

 

Probability of Rolling Dice and Spinning a Colour

Event A:  Toss Dice

Event B:  Spin Wheel

Toss two six-sided die and spin a five sector color spinner.   What is the probability of a particular number and color being selected?

Solution:

You can use real dice and spinner or use the virtual ones.  The probability of of any number being tossed is 1/6, while the probability of the spinner stopping on each color is 1/5.  Examples:

P(5, green) means the probability of tossing 5 and spinning green

P(3, red) means the probability of tossing 3 and spinning red

Complete 180 trials and complete the experimental probability.

Two Events Experimental Probability Theoretical Probability
P(5, green) = /180 4/36 x 1/5 = 4/180 = 0.0222... = 2.2%
P(3, red) = /180 2/36 x 1/5 = 2/180 = 0.0111... = 1.1%

 

 

Probability of Drawing Two Cards

 

Press Reload/Refresh if the calculator does not show properly.

To be independent, you must put the first card back, before drawing the second.  This is equivalent to drawing from two different decks of cards.

Complete the appropriate number of  trials and complete the experimental probability.

Two Cards selected Experimental Probability Theoretical Probability
P(©,¨) = /16 1/4 x 1/4

1/16 = 6.25%

P(4,7) = /169 1/13 x 1/13

= 1/169 = 0.05%

 

 

Toss 6-sided die, Flip Coin, Spin 5 Sector Spinner, Draw a Card

Event A

Event B

 

Event A

P(A) Event B P(B) Theoretical Probability

P(A,B) = P(A) x P(B)

Toss 3 1/6 Toss 4 1/6 1/6 x 1/6 = 0.028 = 2.8%
Toss 2 1/6 Toss 5 1/6 1/6 x 1/6  = 0.028 = 2.8%
Toss 6 1/6 Flip Tails 1/2 1/6 x 1/2 = 0.083 = 8.3%
Flip heads 1/2 Toss 3 1/6 1/2 x 1/6 = 0.083 = 8.3%
Flip tails 1/2 Spin green 1/5 1/2 x 1/5 = 0.1 = 0.10%
Draw club 1/4 Spin yellow 1/5 1/5 x 1/4 = 0.05 = 5%
Draw 6 1/13 Flip heads 1/2 1/13 x 1/2 = 0.038 = 3.8%
Draw heart 1/4 Flip heads 1/2 1/4 x 1/2 = 0.125 = 12.5%

 

Review:

Free JavaScripts provided
by The JavaScript Source

 

E-Lab: Exploring Independent Events - awesome

Exploring Probability - spinner

Experimental Probability Spinner

Crazy Choices Game

 

Enrichment:

Urn/Tree Diagram

Dependent Event Calculations

Lesson on Probability of Dependent Events

Memory Game

source:  Teilhard 4 Kids

This game is known under many names, "Concentration" for example. Click on two boxes, if they match, they remain showing. When all images show, the game is over. The challenge is to finish in as few moves as possible.

What is the probability of getting a pair on the first two selections?

2/16 x 1/15 = 0.0084 = 0.84%

Pick Two Cards

source:  Deck of Cards applet

 

To be dependent, do not put the first card back, before drawing the second.
Cards Probability
P(5,K)  

1/13 x 1/12 = 0.0064 = 0.64%

P(©,¨)  

13/52 x 13/51 = 0.064 = 6.4%

 

 

Probability of  Dependent Event Calculation

Illustrative Example 1:

Amanda chose three different single digits for her combination lock.  Zero was not one of these digits.  If someone knew she used single digits, what is the probability that someone could make a lucky guess and open her lock?

Solution:

To get an idea of how many combinations there are for 3 nonzero digits.  Click on at least 10 times.

Number of Numbers

Maximum Number Generated

generator source modified from:  Java Goodies, javascript, lottery picks

Someone has a 1 in 9 chance of picking the first number.  Since all of the numbers are different they would have a 1 in 8 and 1 in 7 chance of guessing the second and third number correctly.  The following table summarizes the steps and shows the probability to be 0.2.

Maximum Number Generated Number of Numbers Odds of Guessing Probability

9

3

1/9 x 1/8 x 1/7

0.002 =0.2%

 

Illustrative Example 2:

How would the probability change if the person did not know about the single digits? Explain

Solution:

To calculate probability, you need to understand your options.  For combination locks you would need to know the range of numbers and the number of numbers in the combination and if zero is included in the choices.

If you want to see samples of the following change the Number of Numbers and Maximum Number Generated in the generator included in Example 1.

Maximum Number Generated Number of Numbers Odds of Guessing Probability

10

3

1/10 x 1/9 x 1/8

0.0011 =0.14%

30 3

1/30 x 1/29 x 1/28

0.00004 = 0.004%

60 3

1/60 x 1/59 x 1/58

0.0000048 = 0.00048%

 

Applets

Coin Sample Experiment

Simulation of the Dice Experiment

Simulation of the Card Experiment

Simulation of the Coin Die Experiment

Simulation of the Die Coin Experiment

 
 

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Comments to:  Jim Reed
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