Related Rates Question: How to Solve and Understand Using Equations

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SUMMARY

This discussion focuses on solving a related rates problem involving revenue and production rates. The key equation derived is the total daily revenue, represented as R = q(40 - q/180), where q is the quantity sold. The marginal rate of revenue is calculated as dR/dt = (40 - q/90)(dq/dt). Given that the production rate dq/dt is 40 units per day and q is 180, the resulting revenue change is dR/dt = 1520 dollars per day. Participants clarify the distinction between q and dq/dt, emphasizing the importance of understanding these variables in related rates problems.

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Homework Statement


http://img25.imageshack.us/img25/1937/38821874.jpg


Homework Equations


in the picture


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? pleasezzz!
 
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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.

dq/dt is the product/day right?
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.
 
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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