Cogito
Grade 1 Math · Chapter 3 · Lesson 7
Taking Nothing and Taking All
Some subtractions you can answer without working.
10 problems · about 10 minutes · 1.OA.C.6
What this lesson teaches
The child reasons about n − 0, n − n, and n − (n − 1) structurally rather than by computing.
- Take away 0 and nothing changes.
- Take away all and nothing is left.
- Some answers you can just reason out.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Fact Families: You know 4 + 5 = 9. What is 9 − 4?
Answer 5
Why Same fact, read the other way.
Review — What Changed?: 9 − ? = 6
Answer 3
Why 9 − 3 = 6.
Review — The Hidden Part: Whole 9, one part 4. What is the other part?
Answer 5
Why 4 + 5 = 9.
Review — Taking Away: 7 − 3 = ?
Answer 4
Why 7 − 3 = 4.
Warm Up
Straightforward practice. Get the method working first.
3 problems10 − 10 = ?
Answer 0
Why Take all away and none are left.
4 − 0 = ?
Answer 4
Why Take nothing and you still have 4.
8 − 0 = ?
Answer 8
Why Nothing went away.
Build It Up
The same ideas with more to keep track of.
1 problem5 − 5 = ?
Answer 0
Why They all went away.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problems9 − 8 = ?
Answer 1
Why Nearly all went. Just one stays.
The Empty Plate: There are 6 biscuits. Nobody eats any. How many are left?
Answer 6 biscuits
Why 6 − 0 = 6.