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Math Help - Total Cost calculation

  1. #1
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    Total Cost calculation

    Theresa bought lunch for herself and 2 friends. The cost for each lunch was between $3.95 and $4.80, including tax. Which of the following could be the total cost of the lunches that Theresa bought? A $9 B $13 C $18 D $26 Is the answer to the question above question $13 Total Cost(TC) = Average cost(AC) * Quantity (Q) = ( 3.95 + 4.8)/2 * 3 =13.125 How best can I explain the answer in a simple format to a grade 7 class?
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  2. #2
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    Re: Total Cost calculation

    Not sure if this will make things more confusing or not.

    Let x be the cost of one lunch, we know 3.95<x<4.80 and there are 3 lunches in total so

    3\times 3.95<3x<3\times 4.80

    11.85<3x<14.4 therefore the total cost must be $13 as none of the other options fit within the inequality.
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  3. #3
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    Re: Total Cost calculation

    if its for kids who haven't done inequalities before you could ask them to work out with you what the lowest possible cost is (3.95*3), then what the highest possible cost is (4.8*3), and then note that only $13 is a possible answer.

    which is identical to the previous post, with a gentle introduction
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