Cogito
Grade 1 Math · Chapter 5 · Lesson 9
True or False to Twenty
Now both sides can have sums in them.
10 problems · about 13 minutes · 1.OA.D.7
What this lesson teaches
The child judges equations within 20 that have expressions on both sides, such as 12 − 7 = 3 + 2.
- Both sides can have sums in them.
- Work out one side at a time.
- Then check whether they match.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
5 problemsReview — Missing Numbers to Twenty: 8 + ? = 12
Answer 4
Why 8 + 4 = 12.
Review — Take From Ten in Stories: 11 − 8 = ?
Answer 3
Why 11 − 8 = 2 + 1 = 3.
Review — Taking From Ten: 13 − 9 = ?
Answer 4
Why 13 − 9 = 1 + 3 = 4.
Review — Counting On or Making Ten?: 8 + 2 = ?
Answer 10
Why 8 + 2 = 10.
Review — Start With the Bigger One: 6 + 9 = ?
Answer 15
Why 9 + 6 = 10 + 5 = 15.
Warm Up
Straightforward practice. Get the method working first.
3 problemsIs 13 − 9 = 2 + 2 true?
Answer True. Both are 4.
Why Both sides come to 4.
Is 8 + 7 = 16 true?
Answer False. 8 + 7 is 15.
Why 8 + 7 = 10 + 5 = 15, not 16.
Is 11 − 8 = 1 + 2 true?
Answer True. Both are 3.
Why 11 − 8 is 3. What is 1 + 2?
Build It Up
The same ideas with more to keep track of.
1 problemIs 9 + 4 = 12 true?
Answer False. 9 + 4 is 13.
Why Make a ten from the 9.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
1 problemChecking Both Sides: Is this true? 10 + 5 = 9 + 6
Answer True. Both sides are 15.
Why 10 + 5 = 15 and 9 + 6 = 15, so both sides match.