Answer:
Part-to-part ratios provide the relationship between two distinct groups. For example, the ratio of men to women is 3 to 5, or the solution contains 3 parts water for every 2 parts alcohol.
Part-to-whole ratios provide the relationship between a particular group and the whole populations (including the particular group). For example, 3/5 of the students in the class are girls, or the mixture is 40% rye grass (40% is equivalent to saying 40 of every 100 parts).
