Problem
The graph below shows the relationship between minutes left and days of the month of your cellular phone plan. The relationship can be modeled by the equation $f(x)=-\frac{5}{2} x+60$, where $y$ is the number of minutes left and $x$ is the day of the month. Which statement is true? There is no $x$-intercept or $y$-intercept. The domain is all real numbers. The range is all whole numbers greater than or equal to 0 and less than or equal to 60 The function has no maximum value.
Solution
Step 1 ：Find the x-intercept and y-intercept of the function $f(x)=-\frac{5}{2} x+60$.
Step 2 ：The y-intercept is at $(0, 60)$.
Step 3 ：The x-intercept is at $(24, 0)$.
Step 4 ：The domain of the function is all real numbers.
Step 5 ：The range of the function is all whole numbers greater than or equal to 0 and less than or equal to 60.
Step 6 ：The function has no maximum value.
Step 7 ：\(\boxed{\text{The range is all whole numbers greater than or equal to 0 and less than or equal to 60}}\)
