Ray's New Primary Arithmetic · Lesson LXV · Unit 7: Signs, bigger numbers and mixed problems
65. Adding past 20
Goal: Your child adds a small number to a two-digit number, such as 24 + 2 or 30 + 4.
You'll need
- Bundles or cups of ten and single beans
- A slate, small whiteboard or paper and pencil
What's in the book
Rows of questions such as "How many are 16 + 1? 2 + 16? 16 + 3?" and "How many are 20 + 2? 4 + 30? 40 + 6?"
The lesson, step by step
Use what you know
Show that 6 + 2 = 8, so 16 + 2 = 18, 26 + 2 = 28, 36 + 2 = 38. The ones work the same way in every ten.
Build one
Make 24 with 2 tens and 4 ones. Add 2 ones: 26.
Book rows
Work along the rows on the page, a row at a time.
Afterwards
A row a day until it is easy.