Continuity: Let W be the total oil reserves in year t... What are the units on dW/dt?

[pf1996]

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[tkhunny]

Let W be the total oil reserves in the year t. That is, W represents the total quantity of oil, including whats not discovered on earth during time t, necessarily. assume no new oil is being made, and W is measured by wooden barrels.

a.) what are the units dW/dt?
b.) what is the meaning of dW/dt?
c.) What is its sign?
d.) How would you start estimating derivativees in practice?
e.) what would you need to know to make the above assumptions?

Could you possibly give us a hint were you are with this? a, b, and c are lovely thought questions. What say you?