8th Grade · Expressions & Equations
Constant of Proportionality
8.EE.B.5
Definition
The constant ratio k in a proportional relationship y equals k times x. It equals the unit rate and the slope of the graph.
Teach it
Where it is taught, with guided notes, practice, homework, an exit ticket and an interactive Teacher Deck.
Examples
- If 4 apples cost 12 dollars, k = 12/4 = 3 dollars per apple.
- On the graph, the line rises 3 for every 1 across — k is the slope.
Key rule
k is the unit rate, the slope, AND the value of y when x = 1 — all the same number.
Memory hook
k = y/x, always.