Skill: Add lengths in the same unit

Explanation and Free Practice Resources

The learner understands that lengths measured in the same unit can be combined by adding their numerical measures while retaining the common unit, such as $7$ centimeters plus $5$ centimeters equaling $12$ centimeters. They can represent and reason about these combinations with labeled diagrams, bar models, or number lines, recognizing that unlike units must first be converted; work is limited to whole-number measurements and does not include fractional, decimal, or unit-conversion calculations.

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Detailed Explanation: Add lengths in the same unit

When two lengths use the same unit, add their numbers and keep the unit.

Example: A red ribbon is $7$ centimeters long. A blue ribbon is $5$ centimeters long. How long are they altogether?

Write the lengths with their units:

7\text{ cm}+5\text{ cm}

Add the numbers:

7+5=12

Keep the common unit, centimeters:

7\text{ cm}+5\text{ cm}=12\text{ cm}

A bar model shows the same idea:

\boxed{\phantom{xxx}7\text{ cm}\phantom{xxx}} + \boxed{\phantom{xx}5\text{ cm}\phantom{xx}} = \boxed{\phantom{xxxxx}12\text{ cm}\phantom{xxxxx}}

So, the two ribbons are $(12)$ centimeters long altogether.

Learn by doing: Add lengths in the same unit

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Measurement - Add String Lengths - Centimeters, Answer in Centimeters

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Units Teaching This Skill

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