Final answer:
The equation that relates variables a and b, where a varies inversely with b and a=12 when b=1/3, is a=4/b.
Step-by-step explanation:
If a varies inversely with b, this means that the relationship between a and b can be described by the equation a = k / b, where k is the constant of variation.
Given that a=12 when b=1/3, we can substitute these values into the equation to find k.
So we get 12 = k / (1/3) or 12 = 3k, which implies k=4.
Therefore, the equation that relates a and b is a = 4 / b.