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Which fraction qualifies as a proportion?
ANumber of apples divided by number of oranges
BNumber of apples divided by number of all fruits
CNumber of oranges divided by number of apples
DNumber of hospitals divided by number of clinics
Answer & Solution
Correct answer: B. Number of apples divided by number of all fruits
1. A proportion requires the numerator to be a subset of the denominator.
2. Apples are one kind of fruit, so apples over all fruits satisfies that requirement.
3. Apples over oranges and oranges over apples both compare two separate categories, so neither numerator sits inside its denominator.
4. Hospitals over clinics compares two different things as well, so it is a ratio only.
_Source: CDC Principles of Epidemiology in Public Health Practice (3rd ed., US federal, public domain), Lesson 3 "Measures of Risk", section Properties and uses of proportions_
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