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Math Help - Variables thing with monetary values

  1. #1
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    Variables thing with monetary values

    In January 2006, US first class mail rates increased to 39 cents for the first ounce plus 24 cents for each additional ounce. If Sabrina spent $15.00 on a total of 45 stamps of these two denominations , how many of each denomination did she buy?

    please show working out because that is waht is confusing me =P
    thx in advance
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  2. #2
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    Talking

    Quote Originally Posted by ns2583 View Post
    please show working out because that is waht is confusing me
    You already have "the working out" in the various examples provided in your textbook, your class notes, and whatever other resources you have accessed, so looking at one more worked example is unlikely to change the situation much.

    Instead, let's try working this together. By participating in the process, you will learn, "hands on", how to do this (and thus come to understand all the worked examples you've looked at) and, by reviewing your work and reasoning, we'll be able to "see" where you're actually needing help. So:

    Quote Originally Posted by ns2583 View Post
    In January 2006, US first class mail rates increased to 39 cents for the first ounce plus 24 cents for each additional ounce. If Sabrina spent $15.00 on a total of 45 stamps of these two denominations , how many of each denomination did she buy?
    i) She bought two types of stamps. Pick a variable to stand for one of the types of stamps. Let's say we pick "f" to stand for "one first-ounce stamp".

    ii) Since she bought 45 in total, and "f" of them were first-ounce stamps, how many were left to be the "additional ounce" stamps? Create an expression, in terms of the variable in (i), for the number of additional-ounce stamps.

    iii) The value of one first-ounce stamp is (39)(1) = 39 cents. The value of two is (39)(2) = 78 cents. Create an expression for the value of "f" first-ounce stamps.

    iv) Using reasoning similar to that in (iii), create an expression for the value of the additional-ounce stamps.

    v) Since the total value (in cents) is given as being 1500, and since this total is the sum of the values of the two types of stamps, add the two "value" expressions and set the sum equal to the given total.

    vi) Solve the linear equation for the value of the variable.

    vii) Back-solve to find the requested values.

    If you get stuck, please reply showing how far you have gotten. Thank you!
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  3. #3
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    I also have this exact problem in my Pre-Algebra class.

    I need to use only one variable, so I assigned it as X.

    0.39x I put as the amount of 39 cents stamps
    0.24(15-x) as the amount of 24 cent stamps
    15(45) is the total.

    0.39x + 0.24 (15-x) = 15 (45)

    Would that be how it would be set up? I've got incorrect answers doing it that way.

    TIA
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