Ray's New Primary Arithmetic · Lesson XX · Unit 3: Addition
20. Adding 10 (sums to 20)
Goal: Your child knows by heart every fact that adds 10 to a number from 1 to 10, and uses them in story problems.
You'll need
- About 20 small counters: dried beans, buttons, pennies or pebbles (the book suggests marbles, beans or pebbles)
- A slate, small whiteboard or paper and pencil
What's in the book
The table of facts with 10, from "10 and 1 are 11" to "10 and 10 are 20", with the turned-around facts, then about nine short story problems. The first problem has a worked solution.
The lesson, step by step
Warm up
Ask five quick facts from the earlier tables, out of order. Note any that are slow; they go in tomorrow's warm-up.
Build it with counters
Put out a group of 10. Add 1 more and ask how many. Then start again with 10 and add 2, then 3, and so on.
Say each one as a full sentence: "10 and 1 are 11. 10 and 2 are 12."
Read the table
Open the book page and read the table together. Then your child reads it alone.
Cover and recall
Cover the answers with a card. Ask the facts out of order. Include the turned-around ones: "3 and 10" is the same as "10 and 3".
Story problems
Read the problems on the page aloud, one at a time. They go like this:
I paid 10 cents for ink, and 2 cents for paper: how much did I pay for both?
There are 10 trees in one row, and 4 in another: how many trees in both rows?
Your child answers in a full sentence, the way the worked solution does.
Write a few
Your child writes five facts from this table on the slate from memory.
Wrap up
One last quick round of the three facts that were hardest today.
Afterwards
Two minutes on this table each day until all its facts come instantly, then move on.
Tip
Adding 10 just changes the tens: 10 and 4 are fourteen, one ten and four.