11.1 Compound Events Lesson Objectives Understand compound events. Represent compound events. Vocabulary compound event possibility diagram simple event tree diagram Understand Compound Events. A compound event consists of two or more simple events occurring together or one after another. For example, tossing a coin for heads or rolling a 3 on a six-sided number die are both simple events. But tossing a coin for heads and rolling a 3 on a six-sided number die is a compound event. Example 1 Identify events as simple or compound. ell whether each event is a simple or compound event. State the single event or identify the simple events that form the compound event. a) Getting a number less than 2 or greater than 4 when spinning the spinner once his is a simple event. here is one event: getting a number less than 2 or greater than 4 from one spin of the spinner. 1 2 8 3 7 4 6 5 b) Getting a number less than 2 or greater than 4 when spinning the spinner two times consecutively his is a compound event. here are two simple events: getting a number less than 2 or greater than 4 one after another. c) Getting heads when a coin is tossed and getting a 3 when a six-sided number die is rolled his is a compound event. here are two simple events: getting heads on a coin and a 3 on a six-sided number die. Lesson 11.1 Compound Events 219
Guided Practice ell whether each outcome is from a simple or compound event. If it is a compound event, identify the simple events that form the compound event. 1 Obtaining two heads when two coins are tossed 2 Winning a football game 3 Getting a number less than 4 or greater than 5 when a fair six-sided number die is rolled 4 Rolling two fair six-sided number dice and obtaining a sum of 10 from the throws Represent Compound Events. Suppose you roll a fair six-sided number die and toss a fair coin. he simple events that form this compound event are rolling a number on the number die and tossing the coin for heads and tails. here are six possible outcomes when a number die is rolled. he sample space is {1, 2, 3, 4, 5, 6}. here are two possible outcomes when a coin is tossed. hey are {, }, where denotes the outcome eads, and denotes the outcome ails. he braces { } are used to list the set of possible outcomes in a sample space or outcomes favorable to an event. 220 Chapter 11 Probability
here are many ways to represent and display all the outcomes of a compound event. An organized list for the outcomes of tossing a number die and a coin is shown here. Die 1 1 2 2 3 3 4 4 5 5 6 6 Coin Outcome 1 1 2 2 3 3 4 4 5 5 6 6 A two-way grid or a table is a type of possibility diagram that can help you visualize all the possible outcomes of a compound event. You can also circle or mark the favorable outcomes. List the outcomes for rolling a die on the horizontal axis and the outcomes for tossing a coin on the vertical axis. Note that each intersection of grid lines represents a possible outcome of the compound event. Coin ossed 1 2 3 4 5 6 Number Die Rolled represents heads represents tails hink Math ow can the possibility diagram help you determine the number of possible outcomes in a sample space of a compound event without counting? Because the two simple events occur together, the order of the events is not important. So, you can use a dot ( ) to indicate each possible outcome. From the diagram, you can see that there are 12 possible outcomes in the sample space for this compound event. Notice that the outcomes in the two-way grid are the same as those in the organized list for this sample space. Continue on next page Lesson 11.1 Compound Events 221
Another diagram that is used to display the outcomes of a compound event is a table of ordered pairs. 1 2 3 1 2 3 Spinner 1 Spinner 2 Suppose there are two spinners, with each spinner divided into three equally-sized angles at the center. he row labels and column labels of the table list the outcomes of each simple event. Each possible outcome is written in the diagram as an ordered pair: (first event, second event). You can see that there are 3 3 5 9 possible outcomes in the sample space. Spinner 1 1 2 3 Spinner 2 1 (1, 1) (2, 1) (3, 1) 2 (1, 2) (2, 2) (3, 2) 3 (1, 3) (2, 3) (3, 3) Example 2 Represent all possible outcomes of a compound event. Represent and tell the number of possible outcomes for each compound event described. a) he results of rolling two fair six-sided number dice are added. 2nd oss 1st oss + 1 2 3 4 5 6 1 2 3 4 5 6 7 2 3 4 5 6 7 8 3 4 5 6 7 8 9 4 5 6 7 8 9 10 5 6 7 8 9 10 11 6 7 8 9 10 11 12 Math Note You can write the operation of the compound event at the top left cell of the table to indicate that you are finding the sum of the outcomes of two events. here are 36 possible outcomes. 222 Chapter 11 Probability
b) he two spinners shown below are spun. 1 0 2 1 2 4 Spinner 1 3 Spinner 2 Spinner 1 0 1 2 4 Spinner 2 1 (0, 1) (1, 1) (2, 1) (4, 1) 2 (0, 2) (1, 2) (2, 2) (4, 2) 3 (0, 3) (1, 3) (2, 3) (4, 3) here are 12 possible outcomes. c) One drawer has four shirts: 1 blue, 1 yellow, 1 red, and 1 gray. Another drawer has two pairs of socks: 1 gray and 1 black. A shirt and a pair of socks are taken from its drawer. Socks Gray Black Blue Yellow Red Shirts Gray here are 8 possible outcomes. Guided Practice Represent and tell the number of possible outcomes for each compound event described. 5 he results of tossing two fair coins together 6 he results of rolling two fair six-sided number dice are multiplied. 7 A fair six-sided number die and a fair four-sided number die labeled 1 to 4 are rolled. he results that face down on both number dice are recorded. Lesson 11.1 Compound Events 223
Represent Compound Events Using ree Diagrams. A tree diagram is another type of possibility diagram that can be used to represent a compound event. he tree diagram below represents the outcomes of a simple event, tossing a fair coin. he branches from the node represent all possible outcomes. 1 2 Node 1 2 Branches represents heads represents tails When all the branches represent equally likely outcomes, you can omit labeling the probabilities on the branches. For drawing any tree diagram, you should take note of the following: Each branch starts from the same node. he number of branches indicates the number of outcomes the event has. he outcome for the event is written at the end of a branch. he probability of the outcome of an event is written in parentheses along the branch. he probabilities of the branches from each node must add up to 1. If the coin is tossed twice, one after another, the tree diagram looks like this: 1st oss 2nd oss Outcome (, ) Math Note Listing the outcomes in a column is optional in a tree diagram. You can also (, ) determine the number of outcomes, when all equally likely outcomes are shown, by counting the number of (, ) branches at the last event in the tree. (, ) represents heads represents tails You can see from the tree diagram that there are 4 equally likely possible outcomes. 224 Chapter 11 Probability
Example 3 Represent a compound event using a tree diagram. a) Robyn has a fair spinner and a coin as shown. She first spins the spinner once and then tosses the coin. Draw a tree diagram to represent all possible outcomes. hen tell the number of possible outcomes. R G B First, draw branches for each outcome of the first event, the spinner. he end of each branch becomes a node for the second event, tossing a coin. Spinner Coin Outcome (R, ) R (R, ) (B, ) B (B, ) G (G, ) (G, ) R represents red B represents blue G represents green represents heads represents tails here are 6 possible outcomes in this compound event. hink Math ow would you draw the tree diagram if the two simple events are switched: first, toss heads or tails on the coin, and second, spin a color on the spinner? Continue on next page Lesson 11.1 Compound Events 225
b) Eric has a yellow, a pink, and a green highlighter in his pencil case. e also has 1 red pen and 2 black pens. Eric randomly selects a highlighter and a pen. Draw a tree diagram to represent all possible outcomes. hen tell the number of possible outcomes. ighlighter Pen Outcome R (Y, R) Y B (Y, B) B R (Y, B) (P, R) P B (P, B) G B (P, B) R (G, R) B (G, B) B (G, B) Y represents yellow P represents pink G represents green R represents red B represents black here are 9 possible outcomes in this compound event. hink Math Are the outcomes shown at the end of the branches equally likely to occur? Explain. Guided Practice For each compound event, draw a tree diagram to represent the possible outcomes. hen tell the number of possible outcomes. 8 Joshua has two bags. he first bag contains 2 blue beads and 1 green bead. he second bag contains 3 lettered cards with the letters P, Q, and R. Joshua randomly takes an item from the first bag, and then from the second bag. 9 A fair coin is tossed, and then a fair four-sided color die with faces painted yellow, green, blue, and black is rolled. he color facing down is the result recorded. 226 Chapter 11 Probability
Practice 11.1 ell whether each statement is rue or False. 1 Selecting the letter A from the word PROBABILIY is a compound event. 2 Selecting the letter B from the word BASEBALL and then from the word ABLE is a simple event. 3 ossing a fair six-sided number die to get either an even number or a five is a compound event. 4 Umberto has 3 red cards and 4 blue cards. Drawing two red cards in a row, without replacing the first card before drawing the second card, is a compound event. ell whether each event is a simple or compound event. If it is a compound event, identify the simple events that form the compound event. 5 Getting a 6 when a fair six-sided number die is rolled. 6 Rolling three fair six-sided number dice and obtaining a sum of 18 from the throws. 7 Getting an eighteen when a fair twenty-sided number die is rolled. 8 Susan has 3 red cards and 4 blue cards. She first draws a blue card. Without replacing the first card, she then draws another blue card. Solve. Show your work. 9 In the top drawer, there are two battery-operated flashlights: red and yellow. In the second drawer, there are three packages of batteries: sizes AA, C, and D. A flashlight and a package of batteries are randomly selected. a) Draw a possibility diagram to represent all possible outcomes. b) ow many possible outcomes are there? 10 wo electronic spinners, A and B, are spun by pressing a button. Spinner A has four sections labeled 1 to 4, while B has three sections, labeled 1 to 3. Spinner B, due to a technical error, will never land on number 2 if spinner A lands on a 4. a) Draw a possibility diagram to represent all possible outcomes. b) ow many possible outcomes are there? Lesson 11.1 Compound Events 227
11 Winston has two boxes. he first box has 3 black pens and 1 red pen. he second box has 1 green ball and 1 yellow ball. Draw a tree diagram to represent all possible outcomes for randomly drawing a pen and a ball from each box. hen tell the number of possible outcomes. 12 Seraphina first tosses a fair six-sided number die. She then tosses a fair coin. Draw a tree diagram to represent all possible outcomes. 13 A game was designed such that a participant needs to accomplish 2 rounds to be considered the overall winner. he first round is to roll a 4 from a fair four-sided number die labeled 1 to 4. he result recorded is the number facing down. he second round is to randomly draw a red ball from a box of 2 differently colored balls. a) Draw a tree diagram to represent all possible outcomes. b) ow many possible outcomes are there? c) If the participant first draws the colored ball and then rolls the four-sided number die, will the number of possible outcomes be the same? Draw a tree diagram to explain your reasoning. 14 Zoe first rolls a fair four-sided number die labeled 1 to 4. hen she rolls another fair four-sided number die labeled 2 to 5. he results recorded are the numbers facing down. a) Draw a possibility diagram to find the number of favorable outcomes for an odd sum. b) Draw a possibility diagram to find the number of favorable outcomes for a difference greater than 2. 228 Chapter 11 Probability