Cogito
Grade 1 Math · Chapter 10 · Lesson 2
Two-Bar Tape Diagrams
Draw a comparison as two bars from the same starting line.
10 problems · about 13 minutes · 1.OA.A.1
What this lesson teaches
The child represents a comparison problem with two labelled tapes and marks the difference.
- Draw both bars from the same start line.
- The extra length is the difference.
- Label both bars so you know which is which.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — How Many More? How Many Fewer?: 10 birds and 6 cats. How many more birds?
Answer 4
Why 10 − 6 = 4.
Review — Telling Time to the Half Hour: How many minutes is half an hour?
Answer 30
Why Half an hour is 30 minutes.
Review — Telling Time to the Hour: Short hand on 4, long hand up. What hour?
Answer 4
Why It is 4 o’clock.
Review — Fourths and Quarters: How many fourths make one whole?
Answer 4
Why 4 fourths make the whole.
Warm Up
Straightforward practice. Get the method working first.
3 problemsBars of 15 and 8. What is the difference?
Answer 7
Why 15 − 8 = 7.
Why must both bars start at the same line?
Answer Otherwise you cannot see the extra bit.
Why A shared start line is what makes the extra length mean something.
Bars of 18 and 11. What is the difference?
Answer 7
Why 18 take away 11.
Build It Up
The same ideas with more to keep track of.
1 problemBars of 20 and 14. What is the difference?
Answer 6
Why 20 take away 14.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsBars of 13 and 13. What is the difference?
Answer 0
Why The bars match exactly.
Collecting Shells: Ana has 16 shells. Leo has 12. How many more does Ana have?
Answer 4 more
Why 16 − 12 = 4.