Proportional Relationships & Constant of Proportionality
Aligned to 7.RP.A.2 — Common Core State Standards for Mathematics.
What this lesson teaches
Two quantities are proportional if their ratio is always the same constant, k. Then y = kx. On a graph it's a straight line through the origin.
Worked example
If 4 tickets cost $52, then k = 52 ÷ 4 = 13 ($/ticket). The rule is y = 13x, so 9 tickets cost 13 × 9 = $117.
Practice questions
- A recipe uses 2 cups flour per 3 cookies-dozen. Find k and the equation.
- Is y = 3x + 1 proportional? Why or why not?
- If 6 m of rope weighs 9 kg, how much does 10 m weigh?
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Relaciones Proporcionales y Constante de Proporcionalidad
Dos cantidades son proporcionales si su razón siempre es la misma constante, k. Entonces y = kx. En una gráfica se representa como una línea recta que pasa por el origen.
Ejemplo: Si 4 boletos cuestan $52, entonces k = 52 ÷ 4 = 13 ($/boleto). La regla es y = 13x, así que 9 boletos cuestan 13 × 9 = $117.
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