Ray's New Intellectual Arithmetic · Lesson VII · Unit 1: Adding and subtracting in your head
7. The subtraction table
Goal: Your child knows the subtraction facts from 2 − 2 up to 22 − 10.
You'll need
- The book page (press “📖 Book page”, or use a printed copy)
- Paper for jotting, though the work is meant to be done in the head
What's in the book
The subtraction table only. There are no story problems.
The lesson, step by step
Warm up
Ask three or four problems from the last lesson again, out of order. Your child answers and says why.
Show the reasoning
Read the table together, then cover the answers and ask out of order.
SaySeven from sixteen leaves nine. How do I know? Because seven and nine are sixteen.
Every subtraction fact is an addition fact backwards.
Work the problems aloud
Read each problem on the page aloud. Your child answers, then explains in a full sentence, the way the book's model solutions do. The problems go like this:
7 from 16?
9 from 15?
6 from 13?
Ask “Why?”
After each answer ask “Why?” or “How do you know?” Ray's wants the reasoning said aloud, not just the number. If your child stalls, go back to the model and say the first half of the explanation together.
Wrap up
Pick the two problems that were hardest today. Tomorrow, start with those as the warm-up.
Afterwards
Do the rest of the lesson's problems over the next day or two, a few at a time. Move on when your child can explain them without help.