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On this page you will find some material about Lesson 13. Read through the material below, watch the videos, and follow up with your instructor if you have questions.
Lesson 13: Basic Concepts of Probability
Table of Contents
Resources
In this section you will find some important information about the specific resources related to this lesson:
- the learning outcomes,
- the section in the textbook,
- the homework,
- supporting video.
Learning Outcomes. (extracted from the textbook)
- Compute theoretical probabilities.
- Compute empirical probabilities.
Topic. This lesson covers
Section 10.1: Basic Concepts of Probability
pages 557-564, ex. 1-5.
Homework.
Practice Homework:
page 565: 1-7, 11-29 odd, 43-47
ALEKS Assignment
Warmup Questions
These are questions on fundamental concepts that you need to know before you can embark on this lesson. Don’t skip them! Take your time to do them, and check your answer by clicking on the “Show Answer” tab.
Warmup Question 1
Solve $$\begin{cases}2x+y=1\\ 3x+2y=3\end{cases}$$
Show Answer Using the Substitution Method
$$\begin{cases}2x+y=1\\ 3x+2y=3\end{cases}$$
$\bigstar$ Substitution Method
From the first equation, we obtain $y=1-2x$. We substitute $y=1-2x$ into the second equation and get
$$3x+2(1-2x)=3$$
$$3x+2-4x=3$$
$$-x=1$$
$$ x=-1$$
So $y=1-2(-1)=3$. The solution set is $\{(-1,3)\}$.
Show Answer Using the Addition Method
$$\begin{cases}2x+y=1\\ 3x+2y=3\end{cases}$$
We multiply both sides of the first equation by $-2$. The system becomes
$$\begin{cases}-4x-2y=-2\\ 3x+2y=3\end{cases}$$
By adding up the two equations, we obtain
$$-x=1,\text{ that is, } x=-1.$$
We substitute $x=-1$ into $2x+y=1$ to obtain $y$:
$$2(-1)+y=1$$
$$-2+y=1$$
$$y=3$$
The solution set is $\{(-1,3)\}$.
Show Answer Using the Graphing Method
$$\begin{cases}2x+y=1\\ 3x+2y=3\end{cases}$$
On the graph below the red line represents $2x+y=1$ and the blue line represents $3x+2y=3$. The lines intersect at $(-1,3)$. The solution set is $\{(-1,3)\}$.
Review
If you are not comfortable with the Warmup Questions, don’t give up! Click on the indicated lesson for a quick catchup. A brief review will help you boost your confidence to start the new lesson, and that’s perfectly fine.
Need a review? Check Lesson 2 for MAT 1275CO.
Quick Intro
This is like a mini-lesson with an overview of the main objects of study. It will often contain a list of key words, definitions and properties – all that is new in this lesson. We will use this opportunity to make connections with other concepts. It can be also used as a review of the lesson.
A Quick Intro to Systems of Linear Equations
in Three Variables
Key Words. System, linear equations, solution to a system, consistent, inconsistent, the Addition Method.
In the warmup question we solved a system of 2 linear equations and 2 variables using: the Substitution Method, the Addition Method and the Graphing Method.
In this lesson we will see how to solve a system consisting of 3 linear equations and 3 variables. A solution must satisfy the 3 equations simultaneously.
Each equation can be thought of a plane or a line (if it has 2 unknowns). So we are looking for the place(s) where the 3 planes/lines intersect each other. The intersection point is a point that satisfies all three equations. The possibilities are:
$\bigstar$ there is only one solution
$\bigstar$ there are infinitely many solutions
$\bigstar$ there is no solution
When there is no solution, the system is called inconsistent. If there is a solution (no matter how many), the system is said to be consistent.
To solve a system in 3 variables, we use the Addition Method in order to eliminate one variable and obtain a system of 2 equations in 2 variables.
Video Lesson
Many times the mini-lesson will not be enough for you to start working on the problems. You need to see someone explaining the material to you. In the video you will find a variety of examples, solved step-by-step – starting from a simple one to a more complex one. Feel free to play them as many times as you need. Pause, rewind, replay, stop… follow your pace!
Video Lesson
A description of the video
In the video you will see how to solve
$$\begin{cases}x+2y-z=-3\\ -x+y-2z=-6\\2x-y-z=1\end{cases}$$
Try Questions
Now that you have read the material and watched the video, it is your turn to put in practice what you have learned. We encourage you to try the Try Questions on your own. When you are done, click on the “Show answer” tab to see if you got the correct answer.
Try Question 1
Solve $$\begin{cases}5x-y+3z=6\\ x+y+2z=3\\-x-2y+z=8\end{cases}$$
Show Answer 1
$$\begin{cases}5x-y+3z=6 \qquad\text{(A)}\\ x+y+2z=3\qquad\text{(B)}\\-x-2y+z=8\qquad\text{(C)}\end{cases}$$
Consider:
$$\begin{cases}x+y+2z=3\qquad\text{(B)}\\-x-2y+z=8\qquad\text{(C)}\end{cases}$$
Adding (B) and (C) eliminates $x$:
$$-y+3z=11\qquad\text{(D)}$$
Now consider (A) and (B):
$$\begin{cases}5x-y+3z=6\qquad\text{(A)}\\ x+y+2z=3\qquad\text{(B)}\end{cases}$$
Multiply (B) by $-5$ to eliminate $x$:
$$\begin{cases}5x-y+3z=6\qquad\text{(A)}\\ -5x-5y-10z=-15\qquad\text{(-5B)}\end{cases}$$
Adding the two equations gives:
$$-6y-7z=-9\qquad\text{(E)}$$
Consider the system consisting of (D) and (E)
$$\begin{cases}-y+3z=11\qquad\text{(D)}\\-6y-7z=-9\qquad\text{(E)}\end{cases}$$
and solve for $y$ and $z$. Multiply (D) by $-6$:
$$\begin{cases}6y-18z=-66\qquad\text{(-6D)}\\-6y-7z=-9\qquad\text{(E)}\end{cases}$$
Adding the two equations gives $-25z=-75$, so $z=3$. By (D), we have
$$-y+3\cdot 3=11$$
$$-y+9=11$$
$$-y=2$$
$$y=-2$$
Substituting $y=-2$ and $z=3$ into (B) gives:
$$x-2+2\cdot 3=3$$
$$x-2+6=3$$
$$x+4=3$$
$$x=-1$$
We have $x=-1$, $y=-2$ and $z=3$.
Check:
$$\begin{cases}5(-1)-(-2)+3\cdot 3\stackrel{?}{=}6 \qquad\checkmark\\ (-1)+(-2)+2\cdot 3\stackrel{?}{=}3\qquad\checkmark\\-(-1)-2(-2)+3\stackrel{?}{=}8\qquad\checkmark\end{cases}$$
So the solution set is $\{(-1,-2,3)\}$.
Try Question 2
Solve $$\begin{cases}3x-y+z=7\\ x+y+z=-3\\4x+2z=4\end{cases}$$
Show Answer 2
$$\begin{cases}3x-y+z=7 \qquad\text{(A)}\\ x+y+z=-3 \qquad\text{(B)}\\4x+2z=4\qquad\text{(C)}\end{cases}$$
Consider:
$$\begin{cases}3x-y+z=7 \qquad\text{(A)}\\ x+y+z=-3 \qquad\text{(B)}\end{cases}$$
Adding (A) and (B) eliminates $y$:
$$4x+2z=4$$
or
$$2x+z=2\qquad\text{(D)}$$
Now consider the system consisting of (C) and (D):
$$\begin{cases}4x+2z=4\qquad\text{(C)}\\ 2x+z=2\qquad\text{(D)}\end{cases}$$
and solve for $x$ and $z$. Divide (C) by $2$:
$$\begin{cases}2x+z=2\\ 2x+z=2\end{cases}$$
Subtracting the two equations gives $0=0$. So the system has infinitely many solutions.
Try Question 3
Solve $$\begin{cases}3x-y+z=7\\ x+y+z=-3\\4x+2z=5\end{cases}$$
Show Answer 3
$$\begin{cases}3x-y+z=7 \qquad\text{(A)}\\ x+y+z=-3 \qquad\text{(B)}\\4x+2z=5\qquad\text{(C)}\end{cases}$$
Consider:
$$\begin{cases}3x-y+z=7 \qquad\text{(A)}\\ x+y+z=-3 \qquad\text{(B)}\end{cases}$$
Adding (A) and (B) eliminates $y$:
$$4x+2z=4$$
or
$$2x+z=2\qquad\text{(D)}$$
Now consider the system consisting of (C) and (D):
$$\begin{cases}4x+2z=5\qquad\text{(C)}\\ 2x+z=2\qquad\text{(D)}\end{cases}$$
and solve for $x$ and $z$. Multiply (D) by $2$:
$$\begin{cases}4x+2z=5\\ 4x+2z=4\end{cases}$$
Subtract the two equations to get $0=1$, which is not possible. So there is no solution.
Homework
You should now be ready to start working on the homework problems. Doing the homework is an essential part of learning. It will help you practice the lesson and reinforce your knowledge.
WeBWork
It is time to do the homework on WeBWork:
$3\times 3$-Systems
When you are done, come back to this page for the Exit Questions.
Exit Questions
After doing the WeBWorK problems, come back to this page. The Exit Questions include vocabulary checking and conceptual questions. Knowing the vocabulary accurately is important for us to communicate. You will also find one last problem. All these questions will give you an idea as to whether or not you have mastered the material. Remember: the “Show Answer” tab is there for you to check your work!
Exit Questions
- What does it mean to solve a system of equations?
- What is the purpose of the Method of Addition?
- What is the graphical description of the system of linear equations?
$\bigstar$ Solve the system of equations $$\begin{cases}2x+y-z=4\\x+2y+2z=1\\3x-y+2z=0\end{cases}$$
Show Answer
\[\begin{cases}2x+y-z=4\qquad\text{(A)}\\x+2y+2z=1 \qquad\text{(B)}\\ 3x-y+2z=0 \qquad\text{(C)}\end{cases}\]
We start by eliminating $y$ from (A) and (B). Multiply (A) by $-2$ and keep (B).
$$\begin{cases}-4x-2y+2z=-8 \qquad\text{(-2A)}\\ x+2y+2z=1 \qquad\text{(B)}\end{cases}$$
Adding these two equations gives
$$ -3x+4z=-7\qquad\text{(D)}.$$
Now consider (A) and (C).
$$\begin{cases}2x+y-z=4 \qquad\text{(A)}\\ 3x-y+2z=0\qquad\text{(C)}\end{cases}$$
To eliminate $y$, we add these two equations and obtain
$$5x+z=4\qquad\text{(E)}.$$
Consider the system with equations (D) and (E):
$$\begin{cases}-3x+4z=-7\qquad\text{(D)} \\5x+z=4 \qquad\text{(E)}\end{cases}$$
and solve for $x$ and $z$. Multiply (E) by $-4$:
$$\begin{cases} -3x+4z=-7 \qquad\text{(D)}\\ -20x-4z=-16\qquad\text{(-4E)}\end{cases}$$
Addding these equations gives
$$-23x=-23$$
$$x=1$$
Substitute $x=1$ into (E):
$$5x+z=4$$
$$5\cdot 1+z=4$$
$$5+z = 4$$
$$z=-1$$
Now substitute $x=1$ and $z=-1$ into (A):
$$2(1)+y-(-1)=4$$
$$2+y+1=4$$
$$3+y=4 $$
$$y=1$$
So $x=1$, $y=1$, $z=-1$.
Check:
$$\begin{cases}2x+y-z=4\\x+2y+2z=1\\3x-y+2z=0\end{cases}$$
$$\begin{cases}2(1)+1-(-1)\stackrel{?}{=}4 \quad\checkmark\\1+2(1)+2(-1)\stackrel{?}{=}1\quad\checkmark\\3(1)-1+2(-1)\stackrel{?}{=}0\quad\checkmark \end{cases}$$
The solution set is $\{(1,1,-1)\}$
Need more help?
Don’t wait too long to do the following.
Need more help?
Don’t wait too long to do the following.
- Watch the additional video resources.
- Talk to your instructor.
- Form a study group.
- Visit a tutor. For more information, check the tutoring page.