Exam 7: Systems of Equations and Matrices

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Find the inverse matrix of A. - A=[05054152108104512040]A = \left[ \begin{array} { r r r r } 0 & 5 & 0 & - 5 \\4 & 15 & - 2 & - 10 \\8 & 10 & - 4 & - 5 \\12 & 0 & - 4 & 0\end{array} \right]

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Find the indicated sum or difference, if it is defined. - [150484][217442]\left[ \begin{array} { r r } - 1 & 5 \\0 & 4 \\8 & - 4\end{array} \right] - \left[ \begin{array} { l l } 2 & 1 \\7 & 4 \\4 & 2\end{array} \right]

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{x2+y2=25x+y=7\left\{ \begin{array} { l } x ^ { 2 } + y ^ { 2 } = 25 \\x + y = 7\end{array} \right.

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Find the indicated matrix. -Let A=[3325]A = \left[ \begin{array} { l l } 3 & 3 \\ 2 & 5 \end{array} \right] and B=[0416]B = \left[ \begin{array} { r r } 0 & 4 \\ - 1 & 6 \end{array} \right] . Find 2A+B2 A + B .

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first two games of the season. Write a matrix containing the total number of points and rebounds for each of the starting five. Game 1 Points Rebounds Levy 20 3 Cowens 16 5 Williams 8 12 Miller 6 11 Jenkins 10 2 Game 2 Points Rebounds Levy 18 4 Cowens 14 3 Williams 12 9 Miller 4 10 Jenkins 10 3 A) [562]\left[ \begin{array} { l l } 5 & 62 \end{array} \right] В) [73830821202110520]\left[ \begin{array} { r r } 7 & 38 \\ 30 & 8 \\ 21 & 20 \\ 21 & 10 \\ 5 & 20 \end{array} \right] C) [38730820211021205]\left[ \begin{array} { r r } 38 & 7 \\ 30 & 8 \\ 20 & 21 \\ 10 & 21 \\ 20 & 5 \end{array} \right] D) [625][ 625 ] Answer: C -In a certain state, it is determined that 87% of all registered Republicans vote for Republican candidates, with the remainder voting for Democratic candidates. It is also determined that 84% of all registered Democrats vote For Democratic candidates, with the remainder voting for Republican candidates. The percent of voters predicted to vote For each party in the next election is given by [RD]=[0.870.160.130.84][xy]\left[ \begin{array} { l } \mathrm { R } \\\mathrm { D }\end{array} \right] = \left[ \begin{array} { l l } 0.87 & 0.16 \\0.13 & 0.84\end{array} \right] \left[ \begin{array} { l } \mathrm { x } \\\mathrm { y }\end{array} \right] where x is the percent of registered Republicans and y is the percent of registered Democrats. If  If x=53% and y=\text { If } x = 53 \% \text { and } y = 47%, What percent of voters are predicted to vote for Democratic candidates in the next election? Round your answer To the nearest percent.

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Solve using Cramer's rule, if possible. If it is not possible, state whether the system is inconsistent or has infinitely many solutions. - {4x+3y=32x+y=1\left\{ \begin{array} { l } 4 x + 3 y = 3 \\2 x + y = - 1\end{array} \right.

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{x2+y2=13xy=1\left\{ \begin{array} { l } x ^ { 2 } + y ^ { 2 } = 13 \\x - y = 1\end{array} \right.

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Find the value of the determinant. - 1123\left| \begin{array} { c c } - 1 & 1 \\ 2 & 3 \end{array} \right|

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Use an inverse matrix to find the solution to the system. -Two phone companies compete for customers in a city. Company 1 retains 3/43 / 4 of its customers and loses 1/41 / 4 of its customers to Company 2. Company 2 retains 5/65 / 6 of its customers and loses 1/61 / 6 to Company 1 . If we represent the fraction of the market held last year by [ab]\left[ \begin{array} { l } a \\ b \end{array} \right] , where aa is the number the that Company 1 had last year and bb is number that Company 2 had last year, then the number that each company will have this year can be found by tl following matrix equation. [AB]=[3/41/61/45/6][ab]\left[ \begin{array} { l } \mathrm { A } \\\mathrm { B }\end{array} \right] = \left[ \begin{array} { l l } 3 / 4 & 1 / 6 \\1 / 4 & 5 / 6\end{array} \right] \left[ \begin{array} { l } \mathrm { a } \\\mathrm { b }\end{array} \right] If Company 1 has A=81,000\mathrm { A } = 81,000 customers and Company 2 has B=153,000\mathrm { B } = 153,000 customers this year, then how many customers did Company 2 have last year?

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Either the dimensions of two matrices or the matrices themselves are given. Find the dimensions of the product AB and the product BA. If either is not defined, say so. - AA is 4×44 \times 4 ; B is 4×44 \times 4 .

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first two games of the season. Write a matrix containing the total number of points and rebounds for each of the starting five. Game 1 Points Rebounds Levy 20 3 Cowens 16 5 Williams 8 12 Miller 6 11 Jenkins 10 2 Game 2 Points Rebounds Levy 18 4 Cowens 14 3 Williams 12 9 Miller 4 10 Jenkins 10 3 A) [562]\left[ \begin{array} { l l } 5 & 62 \end{array} \right] В) [73830821202110520]\left[ \begin{array} { r r } 7 & 38 \\ 30 & 8 \\ 21 & 20 \\ 21 & 10 \\ 5 & 20 \end{array} \right] C) [38730820211021205]\left[ \begin{array} { r r } 38 & 7 \\ 30 & 8 \\ 20 & 21 \\ 10 & 21 \\ 20 & 5 \end{array} \right] D) [625][ 625 ] Answer: C -Momma's Ice Cream Shop sells three types of ice cream (soft-serve, chunky, and nonfat) at its three locations. The table below shows the number of gallons of each type sold per day at each location. Gallons Sold Soft-serve Chunky Nonfat Location I 29 80 30 Location II 24 90 35 Location III 60 120 40 The income per gallon for soft-serve, chunky, and nonfat ice cream is $4, $6, and $8, respectively. Create two Matrices to represent these data, and use matrix multiplication to find a matrix that gives the daily income at Each location.

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{xy+z=8x+y+z=6x+yz=12\left\{ \begin{array} { l } x - y + z = 8 \\x + y + z = 6 \\x + y - z = - 12\end{array} \right.

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Find the indicated matrix. -Let A=[3302]\mathrm { A } = \left[ \begin{array} { r r } - 3 & 3 \\ 0 & 2 \end{array} \right] . Find 3 A3 \mathrm {~A} .

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Find the inverse matrix of A. - A=[1302]A = \left[ \begin{array} { r r } - 1 & 3 \\0 & - 2\end{array} \right]

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The following system does not have a unique solution. Solve the system. - {xy+z=8x+y+z=63x+y+3z=10\left\{ \begin{array} { c } x - y + z = 8 \\x + y + z = 6 \\3 x + y + 3 z = 10\end{array} \right.

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Either the dimensions of two matrices or the matrices themselves are given. Find the dimensions of the product AB and the product BA. If either is not defined, say so. - A=[132];B=[132]A = \left[ \begin{array} { r } 1 \\- 3 \\2\end{array} \right] ; B = \left[ \begin{array} { r } - 1 \\3 \\2\end{array} \right]

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Use an inverse matrix to find the solution to the system. - {x1+x3+x4=4x2+x3x4=122x1+2x2+x33x4=234x2+2x4=6\left\{ \begin{aligned}x _ { 1 } + x _ { 3 } + x _ { 4 } & = 4 \\x _ { 2 } + x _ { 3 } - x _ { 4 } & = 12 \\2 x _ { 1 } + 2 x _ { 2 } + x _ { 3 } - 3 x _ { 4 } & = 23 \\4 x _ { 2 } + 2 x _ { 4 } & = 6\end{aligned} \right.

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Some people must eat a low-sodium diet with no more than 2000 mg of sodium per day. By eating 1 cracker, 1 pretzel, and 1 cookie, a person would ingest 149 mg of sodium. If a person ate 8 pretzels and 8 cookies, he or she Would ingest 936 mg of sodium. By eating 6 crackers and 7 pretzels, a person would take in 535 mg of sodium. Which of the following statements is true?

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Write the augmented matrix associated with the system. - {2x+2y+7z=578x2y2z=342x+7y+9z=81\left\{ \begin{array} { c } - 2 x + 2 y + 7 z = 57 \\ 8 x - 2 y - 2 z = - 34 \\ - 2 x + 7 y + 9 z = 81 \end{array} \right.

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first two games of the season. Write a matrix containing the total number of points and rebounds for each of the starting five. Game 1 Points Rebounds Levy 20 3 Cowens 16 5 Williams 8 12 Miller 6 11 Jenkins 10 2 Game 2 Points Rebounds Levy 18 4 Cowens 14 3 Williams 12 9 Miller 4 10 Jenkins 10 3 A) [562]\left[ \begin{array} { l l } 5 & 62 \end{array} \right] В) [73830821202110520]\left[ \begin{array} { r r } 7 & 38 \\ 30 & 8 \\ 21 & 20 \\ 21 & 10 \\ 5 & 20 \end{array} \right] C) [38730820211021205]\left[ \begin{array} { r r } 38 & 7 \\ 30 & 8 \\ 20 & 21 \\ 10 & 21 \\ 20 & 5 \end{array} \right] D) [625][ 625 ] Answer: C -Assume that the table below gives the median weekly earnings in 2001 for men and women in various age groups.  Weekly Earnings ($) by Age Group 16242534354445545564 Men 375680520706777 Women 343501505545526\begin{array}{l}\text { Weekly Earnings (\$) by Age Group }\\\begin{array} { l | l | l | l | l | l | } & 16 - 24 & 25 - 34 & 35 - 44 & 45 - 54 & 55 - 64 \\\hline \text { Men } & 375 & 680 & 520 & 706 & 777 \\\text { Women } & 343 & 501 & 505 & 545 & 526\end{array}\end{array} Suppose that, in 2002, the median weekly earnings for men increased by 7% in all age groups and the median weekly earnings for women increased by 4% in all age groups. Wha 2×22 \times 2 2 matrix could be multiplied by the matrix below To find the median weekly earnings in 2002 for men and women in various age groups? [375680520706777343501505545526]\left[ \begin{array} { l l l l l } 375 & 680 & 520 & 706 & 777 \\343 & 501 & 505 & 545 & 526\end{array} \right]

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