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Math Help - Algebra

  1. #1
    Junior Member
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    Algebra

    At the grocery store, Sal buys 7 cans of beans, a jar of peanut butter and 4 cartons of milk, which costs $28.55 total. Hal buys 9 cans of beans, a jar of peanut butter and 5 cartons of milk, which costs $35.30 total. If I buy a can of beans, a jar of peanut butter and a carton of milk, i will pay:
    a 8.10 b 8.15 c 8.20 d 8.25 e 8.30

    this is what i have done so far.
    b--> beans
    p--> peanut butter
    m --> milk carton

    7b + 1p + 4m = 28.55=> 1p = 28.55 - 7b - 4m
    9b + 1p + 5m = 35.30=> 1p = 35.30 - 9b - 5m

    therefore
    35.30 - 9b - 5m = 28.55 - 7b - 4m
    2b + 1m = 6.75

    but i dont know what to do from here, or whether i even started right.
    help please ?
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  2. #2
    Master Of Puppets
    pickslides's Avatar
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    If you have 3 unknowns you need at least 3 equations.

    You have 2 equations with 3 unknowns.

    Do you have any further information?
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  3. #3
    No one in Particular VonNemo19's Avatar
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    Detroit, MI
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    Solve the system

    m=\frac{6.75}{2b} right?

    go substitute that back in the equation



    =

    and solve!
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