Final answer:
The distance formula that shows joint variation is d = r * t. This formula demonstrates joint variation because the distance, d, is directly proportional to both the rate, r, and the time, t.
Step-by-step explanation:
The distance formula that shows joint variation is d = r * t. This formula demonstrates joint variation because the distance, d, is directly proportional to both the rate, r, and the time, t. This means that as the rate or time increases, the distance also increases.