Beginning Algebra With Applications, Chapter 5, 5.5, Section 5.5, Problem 6

The table below shows the United States Department of Agriculture limit on saturated fat intake, in grams. Write a relation where the first coordinate is a person's daily Calorie intake and the second coordinate is the limit on saturated fat intake. Is the relation a function?

$\begin{array}{|c|c|}
\hline\\
\text{Daily calories} & \text{Saturated Fat} \\
& \text{(in grams)} \\
\hline \\
1600 & 18 \\
\hline \\
2000 & 20 \\
\hline \\
2200 & 24 \\
\hline \\
2500 & 25 \\
\hline \\
2800 & 31 \\
\hline
\end{array} $

The table can be written as the relation

$\{ (1600,18), (2000,20), (2200,24), (2500,25), (2800,31) \}$

Where the first coordinate is a person's daily calorie intake and the second coordinate is the limit on saturated fat intake. So the relation is a function because no two ordered pairs have the same first coordinate and different second coordinates.