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Homework Help: Word problem polynomial f(x) help

  1. Sep 24, 2011 #1
    1. The problem statement, all variables and given/known data

    2 People build a sandcastle of 36cm by 48cm by 60cm. Later they learn that the box will be smaller; a certain amount will be taken off each of the length width and height

    2. Relevant equations

    3. The attempt at a solution

    a) write a p(x)
    > (36-x) (48-x) (60-x) , also x intercepts if (-x+36) = -(x-36) etc

    b) graph (already did)
    c) the amount of sand in the boc will be 3/5 of the amount in the design) , so i multiplied the l*w*h and then multiplied it by 3/5 and got the answer of 103,680 *3/5 = 62,208

    d) How much was taken off each dimension? ( HOW DO I SOLVE THIS?) anyone? steps plz
  2. jcsd
  3. Sep 24, 2011 #2
  4. Sep 24, 2011 #3


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    Homework Helper
    Gold Member

    Before the answer we'd need a question.
  5. Sep 24, 2011 #4


    Staff: Mentor

    What do you mean, "write a p(x)" - A function that represents what?

    Please give us the exact problem statement.
  6. Sep 24, 2011 #5


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    Homework Helper

    Looks like you'll need to take p(x) and set it equal to 62,208:
    (36 - x)(48 - x)(60 - x) = 62,208

    However, unless you're allowed to solve it graphically using a graphing calculator, I'm not sure you can solve it algebraically (unless you know the cubic formula).
  7. Sep 24, 2011 #6
    Um, Idk, the answer booklet says "approxmiately 9.28" , but yes im on d) and that is the function...

    your method did not work
  8. Sep 24, 2011 #7


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    Staff: Mentor

    If each dimension is reduced by 7.15 you get very close to the desired smaller volume.
  9. Sep 25, 2011 #8


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    Homework Helper

    Hmm, then either the answer booklet has a typo or you copied the problem wrong. I got the same answer that NascentOxygen got.
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