Question

The table shows the ratio between the number of books ordered and their cost:

Number of Books

Cost (dollars)

7

21

8

24

9

27



Find equivalent ratios when the number of books ordered is 1, 2, and 3. Write them as ordered pairs in the form (x-coordinate, y-coordinate). Starting from the origin, explain how to plot the three equivalent ratios on a coordinate grid.

Answer 1

Explanation:

7 books cost $21 (if I understand the description correctly.).

so, the ratio of books to cost seems to be

7/21 = 1/3.

does this hold up with the other data points ?

8/24 = 1/3

8/27 = 1/3

so, yes, that seems to be the defining relationship.

that means that the cost of the books is 3 times the number of books.

therefore, when x = the number of books, y = 3x.

and the ordered pairs would all look like

(x, 3x)

so,

(1, 3)

(2, 6)

(3, 9)

so, this is as indicated above, a line function y = 3x.

you mark the points on the coordinate grid as per their x and y coordinates and draw a line (starting from the origin = (0, 0)) through all these points and up to the end of the coordinate grid indicating that this would go on to infinity.