Big Ideas Math: Modeling Real Life, Grade 8
BI
Big Ideas Math: Modeling Real Life, Grade 8 View details
3. Graphing Proportional Relationships
Continue to next subchapter

Exercise 1 Page 156

The value of x and its corresponding value of y represents an ordered pair that can be plotted in a coordinate plane.

Graph:

Interpretation of Slope: The unit cost of frozen yogurt is 0.75 dollars per ounce

Practice makes perfect
We are given an equation that represents the cost of frozen yogurt. y=0.75x Recall that when two quantities x and y are proportional, the relationship can be represented by the following equation.

y=mx Here, m is the constant of proportionality or the slope. If we compare this with the given equation, we can see that the slope of the given equation is equal to m=0.75. Let's graph the linear equation by using a table of values. We will replace x with 1, 2, and 3 to find the value of y.

x y=0.75x y
1 y=0.75( 1) 0.75
2 y=0.75( 2) 1.5
3 y=0.75( 3) 2.25

The value of x and its corresponding value of y represents an ordered pair that can be plotted in a coordinate plane. Let's plot the ordered pairs and draw a line through the points.

As we can see, the given equation shows that the slope m is equal to 0.75. Remember that the slope is the ratio of the vertical change to the horizontal change. m=y_2-y_1/x_2-x_1 In our case, the vertical change represents the cost and the horizontal change indicates the ounces of frozen yogurt. This means that the slope describes that the cost of the frozen yogurt is 0.75 dollars per ounce.