16. Recall that a proportional relationship is a relationship between two quantities in which the ratio of one quantity to the other quantity is constant.

17. Recall that a proportional relationship is a relationship between two quantities in which the ratio of one quantity to the other quantity is constant.
The graph of a proportional relationship is a line through the origin.

18. Recall that a proportional relationship is a relationship between two quantities in which the ratio of one quantity to the other quantity is constant.
The graph of a proportional relationship is a line through the origin.
When ratios between quantities are not constant, a relationship may be linear but not proportional and the graph does not pass through the origin.

38. Compare to;