Using Units to Guide Solutions
Aligned to N-Q.A.1 — Common Core State Standards for Mathematics.
What this lesson teaches
Units carry meaning: tracking them through a calculation tells you whether an answer is set up correctly. When units cancel and leave the ones you want, the operation is right. Choosing sensible scales for a graph or formula keeps the model readable.
Worked example
A car travels 150 miles on 6 gallons. Find miles per gallon. Set up: 150 miles / 6 gallons. Divide: 150/6 = 25. The units are miles/gallon, exactly what 'per gallon' asks for. Answer: 25 miles per gallon.
Practice questions
- A runner covers 400 meters in 50 seconds. Find the speed in meters per second.
- Convert 90 kilometers per hour into meters per second using 1 km = 1000 m and 1 h = 3600 s.
- A recipe needs 3 cups of flour per 12 cookies. How many cups are needed for 40 cookies, and what units confirm your setup?
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
Usar unidades para guiar soluciones
Las unidades tienen significado: seguirlas a lo largo de un cálculo indica si el planteamiento es correcto. Cuando las unidades se cancelan y quedan las que buscas, la operación está bien. Elegir escalas sensatas para una gráfica o fórmula mantiene el modelo legible.
Ejemplo: Un auto recorre 150 millas con 6 galones. Halla las millas por galón. Planteamiento: 150 millas / 6 galones. Divide: 150/6 = 25. Las unidades son millas/galón, justo lo que pide 'por galón'. Respuesta: 25 millas por galón.
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