Final answer:
The cost of alcohol varies directly with its volume, represented by the equation C = kv, and the water bill varies directly with cubic meter consumption, represented by w = kn, where k is a constant of proportionality in both equations.
Step-by-step explanation:
To express each statement as a mathematical equation involving direct proportionality:
The cost (C) of alcohol varies directly as its volume (v) in milliliters can be written as C = kv, where k is a constant of proportionality.
The water bill (w) is directly proportional to the number of cubic meter consumption (n) can be written as w = kn, where k is a different constant of proportionality
These equations follow the general principle of directly proportional relationships where one quantity varies linearly with another. In such cases, the equation is usually of the form y = kx, where y is the dependent variable, x is the independent variable, and k is the constant of proportionality.