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Homework Help: Releated rates question

  1. Oct 24, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img25.imageshack.us/img25/1937/38821874.jpg [Broken]

    2. Relevant equations
    in the picture

    3. The attempt at a solution
    im really confused!
    im not sure if i did it right in the picture but i pretty much guessed them all.. (with thinking obviously)
    the first one is easy because its just multiplying the whole equation by q..
    dq/dt is the product/day right? so 180..
    for some reason, i think that q=40 and i cannot explain why not 180
    can someone please explain the problem to me? plzzzz!
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 24, 2009 #2


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    Science Advisor

    Yes, since selling q things for p dollars per thing, you make pq dollars, the total daily revenue is pq= q(40- q/180)= 40q- q2/180.

    The marginal rate of revenue (as opposed to the average rate of revenue) is dR/dt= dR/dq dq/dt= (40- q/90)(dq/dt) and you are told that "daily production is 180" and that "A company is increasing production at 40 units per day" so q= 180 and dq/dt= 40. dR/dt= (40- 180/90)(40).= (40-2)(40)= 1520 dollars per day on that particular day.

    No. q is the product/day. dq/dt is the rate of change of production per day and you are told that it is 40.
  4. Oct 24, 2009 #3
    oh thanks man!
    i kinda was doing the same thing just had the numbers mixed up.
    and i didnt know that dR/dq = (40- q/90).. i thought its dR/dt...
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