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Math Help - basic matrix

  1. #1
    TNB
    TNB is offline
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    Question basic matrix

    Matrices
    Matrix P shows the no. of pizzas a local pizza parlor sold over a 2 week period. Matrix D shows the revenues of and advetising fees in dollars per pizza.

    No of pizzas sold
    P= cheese bacon 'shrooms
    {231 182 168}
    {241 206 132}

    No of pizzas sold
    D= Revenues Advertising fees
    [ 2.69 .23 ]
    [ 2.71 .25 ]
    [ 2.84 .29 ]
    If matrix K is the product of p and d, which elelment in matrix k represents the total advertising fees for week one?

    K= (P)(D)=
    [ P11 P12]
    [ P21 P22]

    I'm guessing that this is more of a basic matrices knowledge question..
    Either that or i'd have to multiply the matrices by hand -yuck, how tedious-and choose an answer based on the looks of things.

    I need help...

    ..(I need somebody-HELP! Not just anybody-HELP!.. )
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  2. #2
    A riddle wrapped in an enigma
    masters's Avatar
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    Quote Originally Posted by TNB View Post
    Matrices
    Matrix P shows the no. of pizzas a local pizza parlor sold over a 2 week period. Matrix D shows the revenues of and advetising fees in dollars per pizza.

    No of pizzas sold
    P= cheese bacon 'shrooms
    week 1:[231 182 168]
    week 2:[241 206 132]

    No of pizzas sold
    D= Revenues Advertising fees
    [ 2.69 .23 ]
    [ 2.71 .25 ]
    [ 2.84 .29 ]

    If matrix K is the product of p and d, which elelment in matrix k represents the total advertising fees for week one?

    K= (P)(D)=
    [ P11 P12]
    [ P21 P22]
    Hello TNB,

    That would be P12. Here's your product matrix.

    week 1:[1591.73 147.35]
    week 2:[1581.43 145.21]
    Last edited by mr fantastic; January 19th 2009 at 11:58 AM. Reason: No edit - just flagging the reply as being moved from a duplicate post.
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  3. #3
    Super Member
    earboth's Avatar
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    Quote Originally Posted by TNB View Post
    Matrices
    Matrix P shows the no. of pizzas a local pizza parlor sold over a 2 week period. Matrix D shows the revenues of and advetising fees in dollars per pizza.

    No of pizzas sold
    P= cheese bacon 'shrooms
    {231 182 168}
    {241 206 132}

    No of pizzas sold
    D= Revenues Advertising fees
    [ 2.69 .23 ]
    [ 2.71 .25 ]
    [ 2.84 .29 ]
    If matrix K is the product of p and d, which elelment in matrix k represents the total advertising fees for week one?

    K= (P)(D)=
    [ P11 P12]
    [ P21 P22]

    I'm guessing that this is more of a basic matrices knowledge question..
    Either that or i'd have to multiply the matrices by hand -yuck, how tedious-and choose an answer based on the looks of things.

    I need help...

    ..(I need somebody-HELP! Not just anybody-HELP!.. )
    You don't have to do the complete multiplication. What you are looking for is the result of

    first row of P * second column of D = P12

    I'll leave the rest for you.

    EDIT: Too fast for me, masters.
    Last edited by mr fantastic; January 19th 2009 at 11:58 AM. Reason: No edit - just flagging the reply as being moved from a duplicate post.
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  4. #4
    MHF Contributor
    Joined
    Mar 2007
    Posts
    1,240

    Talking

    What do the rows of the first matrix indicate, numbers sold or week in which sold?

    What do the columns of the second matrix indicate?

    You need the sum of the form (number of type sold)*(cost to advertise that type that week) + (number of another type sold)*(cost to advertise that type that week) + (number of last type sold)*(cost to advertise that type that week).

    So which row of P must be multiplied by which column of D? Which entry of K matches this product?

    Have fun!
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