A proportional relationship or not? (7th grade math)
Potatoes cost $0.60 per pound is the rate we start with. Since we have a rate, the relationship between the WEIGHT and the COST (our quantities) is proportional. I make a table of values, and we observe how the various rates in it are equivalent. Then, I write an equation to represent the relationship, and plot the line in the coordinate plane.
In the second part, we look at a table of values and a graph to determine whether a relationship is proportional. The situation itself actually has THREE variables: the number of days, the number of ditches to dig, and the number of workers. Looking at certain two variables of these, is it a proportional relationship or not? (Hint: It can end up being either direct or inverse variation.)
See also
Scaling figures and the scale ratio
Math Mammoth Grade 7 curriculum (pre-algebra)