Ray's New Primary Arithmetic · Lesson XXXII · Unit 4: Subtraction
32. Subtracting 8
Goal: Your child knows by heart every fact that takes 8 from a number up to 18, 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 that take 8 away, up to "8 from 18 leaves 10", then story problems. The first has a worked solution.
The lesson, step by step
Warm up
Five quick facts from the earlier subtraction tables (or, for this first one, from the addition tables).
Build it with counters
Put out 9 beans and take 8 away. How many are left? Then start with 10 and take 8 away, and so on.
Say each fact in full: "8 from 10 leaves 2."
Link to adding
Show that 8 and 3 are 11, so 8 from 11 leaves 3. Every subtraction fact has an addition fact behind it.
Read the table
Read the table on the book page together, then alone.
Cover and recall
Cover the answers and ask the facts out of order.
Story problems
Read the problems aloud. They go like this:
Jane has 10 cents: if she give 8 cents for a hook, how many cents will she still have?
Frank had 13 oranges, and gave 5 to Charles: how many did Frank then have?
Your child answers in a full sentence.
Wrap up
Your child writes three facts from today's table from memory.
Afterwards
Two minutes a day on this table, mixed with the earlier ones.
Tip
If a fact is slow, count up from the smaller number: for 8 from 14, count from 8 up to 14.