A proportional relationship is a relationship between two quantities where their ratio remains constant. This means that if one quantity increases or decreases, the other quantity changes in a way that keeps the ratio the same. For example, if you have 2 apples costing 4 dollars, then 4 apples would cost 8 dollars, maintaining the same ratio of cost to quantity. In mathematical terms, a proportional relationship can be expressed as y = kx , where k is the constant of proportionality. This concept is commonly used in various fields, such as science, economics, and engineering, to model relationships between different variables.