One ten changes everything
Find ten more or ten less without counting each one.
Explore this lesson →8 practice questions · Optional read aloud · Thinking pad
Let’s understand the idea.
- Predict what happens when you add or remove one complete ten.
- The number of extra ones stays the same.
- Ten more than 99 is 109. Ten less than 10 is zero. Explain your prediction, then use the picture to check.
Something to notice
Ask for a prediction before using the model and an explanation of why the ones stay the same. Observe across fresh starting numbers; the picture is a check, not evidence of mental calculation by itself.
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 1 · 1.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.