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Homework Help: Related Rates SeeSaw.

  1. Jan 6, 2008 #1
    1. The problem statement, all variables and given/known data
    A child weighs 34 Kg is seated on a seesaw. While a child who weighs 40 kg is situated on the opposite end of the seesaw. The function B(x)= 34x / 40 gives the distance that the 40 kg child must sit from the center of the seesaw when the 34 kg child sits x meters from the center. The seesaw is 9m long find the average rate of change in distance as the lighter childs distance changes from 1.5m to 2.5meters.

    2. Relevant equations
    I used the quotient rule to find the derivative of the function. Which turns out to be 68 / 80.

    3. The attempt at a solution
    The thing is the derivative is 34/40. Which equals to 0.85.

    The prof gave us the answer which is -1.275. I havent come close to that.

    I used...

    f(x) = f(b) - f(a) / b-a

    I dont know how to tackle the average rate of change.
  2. jcsd
  3. Jan 8, 2008 #2
    you have forgotten to use the given x value.


    34*x/40 = (34 * 1.5) / 40 = 1.275
  4. Jan 8, 2008 #3

    Shooting Star

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    Hi stokes,

    Was the problem formulated as you have given? Are you sure something's not missing?
  5. Jan 8, 2008 #4


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  6. Jan 9, 2008 #5

    Shooting Star

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    stokes, it would be best to take help from your professor.

    And please let us know how he solved it.
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