How is the idea of proportionality best described when one value decreases as another increases?

The idea of proportionality in the context where one value decreases as another increases is best described as inversely proportional. This means that as one quantity increases, the other quantity decreases in such a way that the product of the two remains constant. For example, if the number of workers on a project increases, the time it takes to complete the project tends to decrease, assuming all else remains equal. Inversely proportional relationships are commonly illustrated with equations such as ( x \times y = k ), where ( k ) is a constant.

The other terms do not accurately capture this relationship. Directionally proportional suggests both values move in the same direction, which does not describe the situation accurately. Equally proportional implies a constant ratio or direct relationship, contrary to the decreasing nature described. Multiplicatively proportional is not a standard terminology in this context, and it does not convey the idea that one value decreases as the other increases. Therefore, the concept of inverse proportionality clearly and effectively represents the relationship outlined in the question.