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Solve each problem using two variables and a system of two equations. Solve the system by the method of your choice. Note that some of these problems lead to dependent or inconsistent systems. On Monday the office staff paid a total of S7.77 including tax for 3 coffees and 7 muffins. On Tuesday the bill was \(\$ 14.80\) including tax for 6 coffees and 14 muffins. If the sales tax rate is \(7 \%,\) then what is the price of a coffee and what is the price of a muffin?

Short Answer

Expert verified
The system is inconsistent; no solution exists.

Step by step solution

01

Define Variables

Let the price of a coffee be \( x \) dollars and the price of a muffin be \( y \) dollars.
02

Set Up Equations

From the problem, we know that 3 coffees and 7 muffins cost \( \$7.77 \), and 6 coffees and 14 muffins cost \( \$14.80 \). We express these as two equations: \[ 3x + 7y = 7.77 \] \[ 6x + 14y = 14.80 \]
03

Simplify the System

Notice that the second equation is simply the first equation multiplied by 2. For simplicity, we divide the second equation by 2: \[ 6x + 14y = 14.8 \implies 3x + 7y = 7.4 \]
04

Identify System Type

Compare the simplified system of equations: \[ 3x + 7y = 7.77 \] \[ 3x + 7y = 7.4 \] Since the left-hand sides are identical but the right-hand sides are different, this system is inconsistent.
05

Interpret the Result

An inconsistent system means that there is no solution. This suggests that there might be an error in the given problem's data or information.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Inconsistent Systems
An inconsistent system of equations is one where the equations contradict each other, meaning there is no set of values that can satisfy both equations simultaneously. In simple terms, these systems do not intersect or meet at any point on a graph.
For example, in the given exercise, we had two equations:
1. \( 3x + 7y = 7.77 \) 2. \( 3x + 7y = 7.4 \)On inspection, these equations represent two lines that are parallel to each other. Since parallel lines never intersect, no common solution exists. When you encounter a system where simplified forms of equations have the same left-hand side but different constants on the right-hand side, it’s a clear sign of inconsistency.

Understanding inconsistent systems is crucial because they help us recognize when data or problems may have errors or need re-evaluation.
Dependent Systems
A dependent system of equations is when all equations in the system represent the same line on a graph. This means that there are infinitely many solutions because each point on the line is a solution to all the equations in the system.
Dependent systems occur when one equation can be derived from another through multiplication or division.
For example, suppose you have the following equations:
1. \( 2x + 4y = 8 \)2. \( x + 2y = 4 \)If you multiply the second equation by 2, you get the first equation. This indicates that both equations are essentially expressing the same relationship between x and y. As a result, any ordered pair (x, y) that lies on this line is a solution to both equations.
Understanding dependent systems helps in recognizing cases where problems may have multiple valid answers or infinite solutions.
Linear Equations
Linear equations form the building blocks of systems of equations. They can be written in the form \( ax + by = c \), where \( a \), \( b \), and \( c \) are constants.

Key characteristics of linear equations include:
  • They graph as straight lines on the coordinate plane.
  • They have one or infinitely many solutions, or no solution.
  • The solution to a single linear equation in two variables (x and y) is a pair of values (x, y) that make the equation true.
In solving systems of linear equations, you may encounter three types of solutions:

  • One unique solution: The lines intersect at exactly one point.
  • Infinitely many solutions (dependent systems): The lines overlap completely.
  • No solution (inconsistent systems): The lines are parallel and never meet.
Understanding how to manipulate and solve linear equations is fundamental to working with more complex systems.

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Most popular questions from this chapter

Solve each problem by using a system of three linear equations in three variables. Stocks, Bonds, and a Mutual Fund Marita invested a total of \(\$ 25,000\) in stocks, bonds, and a mutual fund. In one year she earned \(8 \%\) on her stock investment, \(10 \%\) on her bond investment, and \(6 \%\) on her mutual fund, with a total return of \(\$ 1860\). Unfortunately, the amount invested in the mutual fund was twice as large as the amount she invested in the bonds. How much did she invest in each?

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