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A small shoe company took out a loan of $1,500,000 to expand their inventory. Part of the money was borrowed at 7%, part was borrowed at 8%, and part was borrowed at 10%. The amount borrowed at 10% was four times the amount borrowed at 7%, and the annual interest on all three loans was $130,500. Use matrices to find the amount borrowed at each rate.

$150,000 at 7%, $750,000 at 8%, $600,000 at 10%

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Access these online resources for additional instruction and practice with solving systems of linear equations using Gaussian elimination.

Key concepts

  • An augmented matrix is one that contains the coefficients and constants of a system of equations. See [link] .
  • A matrix augmented with the constant column can be represented as the original system of equations. See [link] .
  • Row operations include multiplying a row by a constant, adding one row to another row, and interchanging rows.
  • We can use Gaussian elimination to solve a system of equations. See [link] , [link] , and [link] .
  • Row operations are performed on matrices to obtain row-echelon form. See [link] .
  • To solve a system of equations, write it in augmented matrix form. Perform row operations to obtain row-echelon form. Back-substitute to find the solutions. See [link] and [link] .
  • A calculator can be used to solve systems of equations using matrices. See [link] .
  • Many real-world problems can be solved using augmented matrices. See [link] and [link] .

Section exercises

Verbal

Can any system of linear equations be written as an augmented matrix? Explain why or why not. Explain how to write that augmented matrix.

Yes. For each row, the coefficients of the variables are written across the corresponding row, and a vertical bar is placed; then the constants are placed to the right of the vertical bar.

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Can any matrix be written as a system of linear equations? Explain why or why not. Explain how to write that system of equations.

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Is there only one correct method of using row operations on a matrix? Try to explain two different row operations possible to solve the augmented matrix [ 9 3 1 2    |    0 6 ] .

No, there are numerous correct methods of using row operations on a matrix. Two possible ways are the following: (1) Interchange rows 1 and 2. Then R 2 = R 2 −9 R 1 . (2) R 2 = R 1 −9 R 2 . Then divide row 1 by 9.

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Can a matrix whose entry is 0 on the diagonal be solved? Explain why or why not. What would you do to remedy the situation?

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Can a matrix that has 0 entries for an entire row have one solution? Explain why or why not.

No. A matrix with 0 entries for an entire row would have either zero or infinitely many solutions.

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Algebraic

For the following exercises, write the augmented matrix for the linear system.

8 x −37 y = 8 2 x + 12 y = 3

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    16 y = 4 9 x y = 2

[ 0 16 9 −1 | 4 2 ]

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  3 x + 2 y + 10 z = 3 −6 x + 2 y + 5 z = 13               4 x + z = 18

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   x + 5 y + 8 z = 19       12 x + 3 y = 4 3 x + 4 y + 9 z = −7

[ 1 5 8 12 3 0 3 4 9 | 16 4 −7 ]

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6 x + 12 y + 16 z = 4    19 x −5 y + 3 z = −9               x + 2 y = −8

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For the following exercises, write the linear system from the augmented matrix.

[ −2 5 6 −18    |    5 26 ]

−2 x + 5 y = 5 6 x −18 y = 26

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Questions & Answers

Ayele, K., 2003. Introductory Economics, 3rd ed., Addis Ababa.
Widad Reply
can you send the book attached ?
Ariel
?
Ariel
What is economics
Widad Reply
the study of how humans make choices under conditions of scarcity
AI-Robot
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn Reply
U(x,y) = (x×y)1/2 find mu of x for y
Desalegn
what is ecnomics
Jan Reply
this is the study of how the society manages it's scarce resources
Belonwu
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macroeconomic is the branch of economics which studies actions, scale, activities and behaviour of the aggregate economy as a whole.
husaini
etc
husaini
difference between firm and industry
husaini Reply
what's the difference between a firm and an industry
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firm is the unit which transform inputs to output where as industry contain combination of firms with similar production 😅😅
Abdulraufu
Suppose the demand function that a firm faces shifted from Qd  120 3P to Qd  90  3P and the supply function has shifted from QS  20  2P to QS 10  2P . a) Find the effect of this change on price and quantity. b) Which of the changes in demand and supply is higher?
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factors influencing supply
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what is economic.
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Jan
economics is a science that studies human behaviour as a relationship b/w ends and scares means which have alternative uses
Jan
calculate the profit maximizing for demand and supply
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Why qualify 28 supplies
Milan
what are explicit costs
Nomsa Reply
out-of-pocket costs for a firm, for example, payments for wages and salaries, rent, or materials
AI-Robot
concepts of supply in microeconomics
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economic overview notes
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identify a demand and a supply curve
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i don't know
Parul
there's a difference
Aryan
Demand curve shows that how supply and others conditions affect on demand of a particular thing and what percent demand increase whith increase of supply of goods
Israr
Hi Sir please how do u calculate Cross elastic demand and income elastic demand?
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Practice Key Terms 7

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Source:  OpenStax, College algebra. OpenStax CNX. Feb 06, 2015 Download for free at https://legacy.cnx.org/content/col11759/1.3
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