Cogito
Grade 1 Math · Chapter 6 · Lesson 6
How Much Longer?
Find the difference between two lengths.
10 problems · about 12 minutes · 1.OA.A.1, 1.MD.A.2
What this lesson teaches
The child solves compare-with-difference-unknown problems about lengths.
- The difference is the extra bit.
- Line them up, then count what sticks out.
- If they are the same, the difference is 0.
Warm-Up Review
From earlier lessons. Loosen up before the new work.
4 problemsReview — Why Same-Size Units?: Why must you say which unit you used?
Answer Because a number alone does not say how long.
Why 8 cubes and 8 blocks are different lengths, so the unit matters.
Review — Measuring With Cubes: A stick takes 6 cubes laid end to end. How long is it?
Answer 6 cubes
Why 6 cubes long.
Review — Putting Three in Order: Ropes are 3, 9 and 6 cubes. How long is the longest?
Answer 9
Why 9 is the longest.
Review — Using a Third Thing: A rope is shorter than a string. The string is shorter than a pole. Is the rope shorter than the pole?
Answer Yes.
Why Rope is under string, string is under pole, so rope is under pole.
Warm Up
Straightforward practice. Get the method working first.
3 problemsA 9-cube stick and a 4-cube stick. How much longer is the first?
Answer 5
Why 9 − 4 = 5.
Two ribbons are both 6 cubes. How much longer is one than the other?
Answer 0
Why They are equal, so the difference is 0.
10 cubes and 6 cubes. How much longer?
Answer 4
Why Count up from 6 to 10.
Build It Up
The same ideas with more to keep track of.
1 problem8 cubes and 5 cubes. How much longer?
Answer 3
Why Count up from 5 to 8.
Stretch Yourself
Mixed problems. Work out what kind of question it is before you start.
2 problemsTwo Trains: A red train is 9 cubes. A blue train is 6 cubes. How much longer is the red one?
Answer 3 cubes
Why 9 − 6 = 3.
Jumping: Ana jumps 7 cubes. Leo jumps 4. How much further did Ana jump?
Answer 3 cubes
Why 7 − 4 = 3.