When are x and y considered inversely proportional?

When two quantities, x and y, are considered inversely proportional, it means that as one quantity increases, the other quantity decreases in such a way that their product remains constant. This relationship is mathematically expressed in the form of the equation y = k/x, where k is a constant. This formulation captures the essence of inverse proportionality because it shows that for any given value of x, y will adjust accordingly to keep the product k (the constant) consistent.

In this context, if one were to increase the value of x, y would decrease so that the multiplication of the two (x and y) would always equate to the constant k. This type of relationship is opposed to direct proportionality, where both variables increase or decrease together proportionately.

The other options do not accurately describe the condition for inverse proportionality. For instance, adding two quantities to equal a constant refers to a different type of relationship. Similarly, multiplying to give a product of zero does not fulfill the conditions of proportionality, nor does plotting on a straight line, which typically relates to direct relationships or linear functions instead. Therefore, the correct answer highlights the specific mathematical relationship that defines inverse proportionality.