Describing derivatives in practical terms

[madgab89]

Homework Statement

Suppose C(r) is the total cost of paying off a car loan borrowed at an annual interest rate of r%. What are the units of C '(r)? What are the units of C'(r)? What is its sign?

Homework Equations

C'(r)=dC/dr

The Attempt at a Solution

So, I figured:

C'(r) = dC/dr
Which is dollars over interest rate(?)...which seems kinda awkward to me. I'm wondering if there's a better solution for what the units of C'(r) would be. (dollars per percent interest?)

And I'm not sure what is meant by "What is it's sign"?

 

[Redbelly98]

What are the units of r?

"What is it's sign" means is it positive or negative ... or zero.

 

[madgab89]

r is a %

 

[Redbelly98]

Okay. So the units of C/r would be ... ?