Final answer:
From the given options, b) 'The number of kilometers ridden is a function of the average rate of travel', c) 'The amount of revenue a doughnut company makes is a function of how many doughnuts are sold', and d) 'A town's yearly average crime rate is a function of the year' correctly describe functions.
Step-by-step explanation:
A function in mathematics describes a specific relationship between two sets of data, where to each element in the first set (independent variable), there is a unique element in the second set (dependent variable). When we consider the given statements, we must determine if they can be described by this definition.
- The statement 'A person's income is a function of their weight' does not typically represent a function because there is not a usual direct or unique relationship between a person's weight and their income.
- The number of kilometers ridden is indeed a function of the average rate of travel, assuming consistent travel over a period of time, since there is a direct relationship between speed and distance traveled.
- The amount of revenue a doughnut company makes is a function of how many doughnuts are sold, as there is a direct correlation between the quantity sold and the revenue.
- A town's yearly average crime rate can be considered a function of the year since we can track crime rate changes over different years.
Hence, the correct descriptions of a function from the options provided are b), c), and d).