Final answer:
The constant of proportionality in the equation y = 5/9x is 5/9. It indicates that for every unit increase in x, y will increase by a factor of 5/9.
Step-by-step explanation:
The constant of proportionality in the equation y = ⅓x is the coefficient of the variable x. When we have a direct proportionality between two variables, the equation takes the form y = kx, where k is the constant of proportionality. In this particular case, the constant of proportionality is ⅓, which can also be written as 5/9. This means that for every unit increase in x, y increases by 5/9 units. Remember, in a directly proportional relationship represented graphically by a straight line going through the origin (0, 0), the slope of the line represents the constant of proportionality.