Rewriting a customary measurement as a metric one, or the reverse, so two amounts can be compared.
Example: 80 km ≈ 48 miles
Ratio Reasoning: Convert Measurements Between Systems
I can use ratio reasoning to convert measurements between the customary and metric systems.
Speaking and writing goal: I can explain a conversion between systems using the words conversion factor, approximately, customary, and metric.
What Your Child Is Learning
In this lesson, students practice how to use ratio reasoning to convert measurements between the customary and metric systems. They learn to show their thinking with numbers, pictures, words, or a model. The goal is not just getting an answer. Students should be able to explain why the answer makes sense.
Why This Matters
This math shows up in shopping, recipes, sports scores, speed, discounts, and comparing choices. It helps students decide what is fair, what is a better deal, and how quantities change together.
What It May Look Like In Class
Your child may use the interactive lesson, guided notes, examples from the board, partner talk, and short practice problems. They may be asked to solve, draw a model, label important numbers, and explain their reasoning in a sentence.
How You Can Help At Home
You do not need to teach a new method. Ask your child to read the problem out loud, circle the important numbers, and explain what they tried first. Helpful questions include: What do you know? What are you trying to find? Does your answer make sense?
Apoyo para familias en español
Qué está aprendiendo su hijo/a
En esta lección, su hijo/a practica comparar cantidades y explicar relaciones. Puede usar dibujos, números, palabras o modelos para mostrar su pensamiento. Lo más importante es que pueda explicar por qué su respuesta tiene sentido.
Por qué es importante
Esta matemática aparece en recetas, compras, deportes, descuentos y comparaciones. Ayuda a los estudiantes a decidir qué es justo o cuál opción conviene más.
Cómo puede ayudar en casa
No necesita ser experto/a en matemáticas. Pídale a su hijo/a que lea el problema en voz alta, marque los números importantes y explique su primer paso. Puede preguntar: ¿Qué sabes? ¿Qué necesitas encontrar? ¿Tu respuesta tiene sentido?
Key Vocabulary
The ratio that links a unit in one system to a unit in the other, such as 1 mile to about 1.609 kilometers.
Example: 1 foot = 12 inches
The measurement system used in the United States: inches, feet, miles, ounces, pounds, cups, quarts, gallons.
Example: A gallon of milk
The measurement system used in most of the world, built on tens: centimeters, meters, kilometers, grams, kilograms, liters.
Example: 500 milliliters
Close to, but not exactly equal. Conversions between systems are almost always approximate, so they use the ≈ sign.
Example: 1 mile ≈ 1.6 km
A table of equal ratios used to scale a conversion factor up to the amount you actually need.
Example: juice 2, 4, 6 beside water 3, 6, 9
Try It Together
Pick one or two problems. Let your child explain the first step before opening the answer.
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There are 2 red tiles for every 3 blue tiles. Write the ratio of red to blue.
Show answer
2:3
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A pack of 4 pens costs $8. What is the cost for 1 pen?
Show answer
$2
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What is 25% of 40?
Show answer
10
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A recipe uses 3 cups of flour for 12 cookies. How much flour for 24 cookies?
Show answer
6 cups