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Cogito

Grade 1 Math · Chapter 5 · Lesson 4

Answer Key

Start With the Bigger One

Swap first, then make your ten.

10 problems · about 12 minutes · 1.OA.B.3, 1.OA.C.6

What this lesson teaches

The child uses commutativity to make ten from the larger addend, turning 6 + 9 into 9 + 6.

  • Swapping does not change the total.
  • Start with the bigger number.
  • Then there is less to move.

Warm-Up Review

From earlier lessons. Loosen up before the new work.

4 problems

  1. Review — Making Ten From Eight: 8 + 5 = ?

    Answer 13

    Why 8 + 5 = 10 + 3 = 13.

  2. Review — Making Ten From Nine: 9 + 5 = ?

    Answer 14

    Why 9 + 5 = 10 + 4 = 14.

  3. Review — Adding Three Numbers: 3 + 7 + 5 = ?

    Answer 15

    Why 3 + 7 = 10, then 10 + 5 = 15.

  4. Review — Counting to Twenty and Back: What comes after 18?

    Answer 19

    Why 19 comes after 18.

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. 6 + 9 = ?

    Answer 15

    Why 9 + 6 = 10 + 5 = 15.

  2. 2 + 9 = ?

    Answer 11

    Why 9 + 2 = 10 + 1 = 11.

  3. 3 + 9 = ?

    Answer 12

    Why Think 9 + 3.

Build It Up

The same ideas with more to keep track of.

1 problem

  1. 5 + 8 = ?

    Answer 13

    Why Think 8 + 5.

Stretch Yourself

Mixed problems. Work out what kind of question it is before you start.

2 problems

  1. 4 + 7 = ?

    Answer 11

    Why Think 7 + 4.

  2. The Playground: There are 5 children on the slide and 8 on the swings. How many children in all?

    Answer 13 children

    Why 8 + 5 = 10 + 3 = 13.