You can use the slope-intercept form. What is the relation between the cost of meal and the tip?
Equation: y=1/5x Example interpretation: The tip increases by $0.20 for each dollar spent on the meal.
Practice makes perfect
We are given a graph showing a relation between the tip and the cost of the meal. Since we are given an y-intercept and a point, it will be most convenient to use slope-intercept form.
Equations written in this form follow a specific format.
y= mx+b
In this form, m is the slope of the line and b is the y-intercept. We need to identify these values using the graph. Let's start with the y-intercept.
Finding the y-intercept
Observe the given graph.
We can see that the function intercepts the y-axis at (0, ). This means that the value of b is .
Finding and Interpreting the Slope
To identify the slope m, let's look at the rise and run of the graph.
Traveling to the point (10,2) from the y-intercept requires that we move 10 steps horizontally in the positive direction and 2 steps vertically in the positive direction.
rise/run=2/10=1/5 ⇔ m= 1/5
Since 15 equals 0.20, the slope tells us that the tip increases by $0.20 for each dollar spent on the meal.
Writing the Equation
Now that we have the slope and the y-intercept, we can form our final equation.
y= mx+b
y= 1/5x+ ⇔ y=1/5x
