Introduction to Matrices and Matrix Operations: Apply It 1

  • Understand how to add and subtract matrices
  • Figure out how to multiply a matrix by a number (scalar) to change its scale
  • Learn to multiply two matrices together to find a new matrix

Using Matrices in Real-World Problems

Consider a real-world scenario in which a university needs to add to its inventory of computers, computer tables, and chairs in two of the campus labs due to increased enrollment from the fall 2013 semester to the fall of 2014. They estimate that [latex]15\%[/latex] more equipment is needed in both labs. The school’s current inventory is displayed in the table below.

Lab [latex]A[/latex] Lab [latex]B[/latex]
Computers [latex]15[/latex] [latex]27[/latex]
Computer Tables [latex]16[/latex] [latex]34[/latex]
Chairs [latex]16[/latex] [latex]34[/latex]

Convert the data to a matrix and find the inventory for 2014.

Computer inventory in fall 2013:

[latex]{C}_{2013}=\left[\begin{array}{c}15\\ 16\\ 16\end{array}\begin{array}{c}27\\ 34\\ 34\end{array}\right][/latex]

To calculate how much computer equipment will be needed in 2014, we multiply all entries in matrix [latex]C[/latex] by [latex]0.15[/latex].

[latex]\left(0.15\right){C}_{2013}=\left[\begin{array}{c}\left(0.15\right)15\\ \left(0.15\right)16\\ \left(0.15\right)16\end{array}\begin{array}{c}\left(0.15\right)27\\ \left(0.15\right)34\\ \left(0.15\right)34\end{array}\right]=\left[\begin{array}{c}2.25\\ 2.4\\ 2.4\end{array}\begin{array}{c}4.05\\ 5.1\\ 5.1\end{array}\right][/latex]

We must round up to the next integer, so the amount of new equipment needed is

[latex]\left[\begin{array}{c}3\\ 3\\ 3\end{array}\begin{array}{c}5\\ 6\\ 6\end{array}\right][/latex]

Adding the two matrices as shown below, we see the new inventory amounts.

[latex]\left[\begin{array}{c}15\\ 16\\ 16\end{array}\begin{array}{c}27\\ 34\\ 34\end{array}\right]+\left[\begin{array}{c}3\\ 3\\ 3\end{array}\begin{array}{c}5\\ 6\\ 6\end{array}\right]=\left[\begin{array}{c}18\\ 19\\ 19\end{array}\begin{array}{c}32\\ 40\\ 40\end{array}\right][/latex]

This means

[latex]{C}_{2014}=\left[\begin{array}{c}18\\ 19\\ 19\end{array}\begin{array}{c}32\\ 40\\ 40\end{array}\right][/latex]

Thus, Lab A will have [latex]18[/latex] computers, [latex]19[/latex] computer tables, and [latex]19[/latex] chairs; Lab B will have [latex]32[/latex] computers, [latex]40[/latex] computer tables, and [latex]40[/latex] chairs.

Two club soccer teams, the Wildcats and the Mud Cats, are hoping to obtain new equipment for an upcoming season.The table below, representing the equipment needs of two soccer teams.

Wildcats Mud Cats
Goals [latex]6[/latex] [latex]10[/latex]
Balls [latex]30[/latex] [latex]24[/latex]
Jerseys [latex]14[/latex] [latex]20[/latex]

We are also given the prices of the equipment, as shown in the table below.

Goal [latex]$300[/latex]
Ball [latex]$10[/latex]
Jersey [latex]$30[/latex]

How can we find the total cost for the equipment needed for each team?