We have the equation:
[tex]r=\frac{d}{t}[/tex]
If d increases, given that t stays constant. then r will increase too. Then, they vary directly.
If t increases, given that d stays constant, then r will decrease. Then, they vary inversely.
We can summarize it as: r varies directly with d and inversely with t.
Answer: r varies directly with d and inversely with t [third option]
