Question

4
the graph below shows the average miles per gallon marie’s new car gets driving on the highway.

what is the unit rate of the graph?
a. 30 miles per gallon
b. 15 miles per gallon
c. 1.5 miles per gallon
d. 20 miles per gallon

Explanation:

Step1: Recall unit rate definition

Unit rate is slope of the line, calculated as $\frac{\text{change in } y}{\text{change in } x}$.

Step2: Identify two points on the line

From the graph, when $x = 3$ (gallons), $y = 60$ (miles); or $x = 6$, $y = 120$. Let's use $(0,0)$ and $(3, 60)$.

Step3: Calculate the slope (unit rate)

Slope $= \frac{60 - 0}{3 - 0} = \frac{60}{3} = 20$? Wait, no, wait. Wait, looking at the graph again, when $x = 3$, $y = 60$? Wait, no, the grid: each x - grid is 3? Wait, no, x - axis is gallons, with marks at 0, 3, 6, 9, 12, 15. Y - axis: 0, 30, 60, 90, 120, 150. Wait, when x = 3 (gallons), y = 60? No, wait, the line passes through (3, 60)? Wait, no, let's check the points. At x = 1 (gallon), what's y? Wait, maybe I misread. Wait, the line goes through (3, 60)? No, wait, when x = 3, y = 60? Wait, no, let's take x = 3, y = 60. Then unit rate is 60/3 = 20? Wait, but the options have D as 20 miles per gallon. Wait, maybe my initial point was wrong. Wait, let's check again. The graph: when x = 3 (gallons), y = 60 (miles)? No, wait, the y - axis is miles, with each grid line at 30, 60, 90, etc. So at x = 3 (gallons), y = 60 miles? Then 60 miles / 3 gallons = 20 miles per gallon. So the unit rate is 20 miles per gallon.

Answer:

D. 20 miles per gallon