Use addition to subtract
Subtract within twenty by finding a missing part or crossing ten.
Explore this lesson →10 practice questions · Optional read aloud · Thinking pad
Let’s understand the idea.
- Subtraction and addition describe the same part-whole relationship.
- Ask: what belongs with the amount taken away to make the starting amount? Or use ten as a stopping place.
- Check by adding the answer and the amount taken away. Their sum should be the original whole.
Something to notice
Ask which facts the learner recalls and which they derive, and revisit them over time in varied contexts. There is no speed score. A correct untimed answer does not prove automatic recall or fluency; the app records practice and support, not a claim that this standard is mastered.
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.OA · 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.