Different grouping, same amount?
Explain why valid place-unit exchanges preserve addition and subtraction.
Explore this lesson →8 practice questions · Optional read aloud · Thinking pad
Let’s understand the idea.
- Changing how units are grouped can keep the same value, but only if the exchange is fair.
- One hundred equals ten tens. One ten equals ten ones. Swapping a hundred for just ten ones would lose value.
- Use the values in a picture or an equation to justify a strategy.
Something to notice
Ask the learner to explain why an exchange keeps the same value and connect their own drawing to a written method. Encourage different valid strategies. Untimed typed accuracy with worked models does not establish fluent independent calculation or explanation.
Try it. Change it. Explain it.
Open the lesson to use its pictures and controls. In How it works, connect the picture to the idea. In Play & discover, change the quantities and notice what stays the same. In Your turn, answer questions and use the explanation to check your reasoning.
You can ask for help, draw on the thinking pad, or listen to the question and answer options. Progress distinguishes independent work from work completed with help.
Let’s try it →Curriculum connection
Grade 2 · 2.NBT · US Common Core
This lesson is mapped to these standards. A completed activity is practice evidence, not a claim of mastery. Content is checked against the linked official standards and its mathematical models are tested.