Question

Difficulty: HardMatrices and Matrix Operations

A sporting goods company sells soccer balls and basketballs at two locations, North and South. The matrix AA represents the inventory of these balls at each location:

A=[50304060]A = \begin{bmatrix} 50 & 30 \\ 40 & 60 \end{bmatrix}

where the rows represent the locations (Row 1: North, Row 2: South) and the columns represent the ball types (Column 1: soccer balls, Column 2: basketballs).

The matrix BB represents the price, in dollars, of each type of ball under two different pricing structures (Column 1: regular price, Column 2: sale price):

B=[20152518]B = \begin{bmatrix} 20 & 15 \\ 25 & 18 \end{bmatrix}

where Row 1 represents soccer balls and Row 2 represents basketballs.

Which of the following matrices represents the total revenue, in dollars, the company would collect from selling its entire inventory at each location under both pricing structures?

  1. A
    [1,0004501,0001,080]\begin{bmatrix} 1,000 & 450 \\ 1,000 & 1,080 \end{bmatrix}
  2. B
    [1,6001,5001,9701,830]\begin{bmatrix} 1,600 & 1,500 \\ 1,970 & 1,830 \end{bmatrix}
  3. C
    [250210700480]\begin{bmatrix} 250 & 210 \\ 700 & 480 \end{bmatrix}
  4. [1,7501,2902,3001,680]\begin{bmatrix} 1,750 & 1,290 \\ 2,300 & 1,680 \end{bmatrix}Answer
  5. E
    [1,7501,3802,3001,720]\begin{bmatrix} 1,750 & 1,380 \\ 2,300 & 1,720 \end{bmatrix}

Answer

[1,7501,2902,3001,680]\begin{bmatrix} 1,750 & 1,290 \\ 2,300 & 1,680 \end{bmatrix}
To find the total revenue under both pricing structures at each location, we perform the matrix multiplication ABAB. The entry in row ii, column jj of the resulting matrix corresponds to the revenue generated at location ii under pricing structure jj. Applying the row-by-column multiplication rule gives the correct matrix containing 1,7501,750, 1,2901,290, 2,3002,300, and 1,6801,680.

Step-by-Step Solution

1
Set up the matrix multiplication to compute the total revenue.
The total revenue matrix is represented by the product ABAB, where we multiply the 2×22 \times 2 inventory matrix AA by the 2×22 \times 2 price matrix BB.
Multiplying the quantities of items by their respective unit prices yields the total revenue.
2
Calculate the entries for the first row of the product matrix, representing the North location.
Row 1, Column 1 (North, Regular): 50(20)+30(25)=1,000+750=1,75050(20) + 30(25) = 1,000 + 750 = 1,750.
Row 1, Column 2 (North, Sale): 50(15)+30(18)=750+540=1,29050(15) + 30(18) = 750 + 540 = 1,290.
The first row of matrix AA is multiplied by the columns of matrix BB to find revenues under both pricing structures at the North location.
3
Calculate the entries for the second row of the product matrix, representing the South location.
Row 2, Column 1 (South, Regular): 40(20)+60(25)=800+1,500=2,30040(20) + 60(25) = 800 + 1,500 = 2,300.
Row 2, Column 2 (South, Sale): 40(15)+60(18)=600+1,080=1,68040(15) + 60(18) = 600 + 1,080 = 1,680.
The second row of matrix AA is multiplied by the columns of matrix BB to find revenues under both pricing structures at the South location.
4
Construct the final product matrix from the calculated values.
AB=[1,7501,2902,3001,680]AB = \begin{bmatrix} 1,750 & 1,290 \\ 2,300 & 1,680 \end{bmatrix}
Placing the computed row values in their respective positions yields the completed revenue matrix.

Key Concept

Matrix multiplication is used to combine quantity data and unit cost data systematically across multiple categories and scenarios.
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