Subtraction within 20
Take Away and Compare
About this book
See it, build it, solve it: addition that makes sense.
Six short modules take young learners from joining two groups of counters to choosing a strategy for story problems. Every module follows the same seven LessonCrest steps, with help that fades as confidence grows.
- Join groups and write equations
- Count on from the bigger number
- Doubles, near doubles and making ten
- Missing parts and what = really means
- Story problems, review pages and an exit check
- Answers that explain why, with help for common mistakes
Look inside
What this book covers
Covered
What this book covers: totals up to 20 with counters, ten-frames, number paths, bar models, equations and stories.
Not covered
Not covered here: two-digit adding and regrouping (they come after place value).
Before you start, you should be able to
- Count up to 20 objects.
- Read the numbers 0 to 20.
- Put two small groups together.
Things to have
Use real objects and read directions aloud whenever needed.
Notice
Pictures in this book are simplified learning models. Check answers with the explanations at the back of the book.
The steps in this book
- Step 1: Get Ready
Check the skills you need before you begin. If something feels tricky, an adult can help you start in the right place.
- Step 2: Learn It
Read a short, clear explanation of the new idea and the words that go with it.
- Step 3: See It
Watch the idea being used, one step at a time, in a worked example.
- Step 4: Try It Together
Practice with prompts and help cues. The help gets smaller as you get stronger.
- Step 5: On Your Own
Practice on your own with different kinds of questions, and explain your thinking.
- Step 6: Look Back
Look back at earlier learning so it stays strong, then check where to go next.
- Step 7: Check and Fix
Check your answers. Each answer explains why, names a common mistake, and shows how to fix it.
What is in the book
The modules
- Module 1: Join groups and write equationsPages 5–14
- Module 2: Count on from a known amountPages 15–24
- Module 3: Doubles and near doublesPages 25–34
- Module 4: Make ten and add the restPages 35–45
- Module 5: Missing parts and equal totalsPages 46–55
- Module 6: Choose a strategy in word problemsPages 56–67
Contents
- Readiness check, pp. 3–4. Before Module 1. Its table tells you where to start.
- Modules, pp. 5–67
- Checkpoints, pp. 14, 24, 34, 45, 55, 67. The last page of each module.
- Mixed review, pp. 68–71. Questions from across the book, mixed together.
- Exit check, pp. 72–73. A last check across the book.
- Reflect and repair, p. 74
- Try again, p. 75. Fresh questions like those in the exit check.
- Extra practice, pp. 76–84
- Answers and explanations, pp. 85–100. Notes in this part are headed “Why”, “Common mistake”, “Help” and “Look for”.