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Cogito

Grade 1 Math · Chapter 5 · Lesson 2

Answer Key

Making Ten From Nine

Move one across and the hard sum turns easy.

10 problems · about 13 minutes · 1.OA.C.6, 1.OA.B.3

What this lesson teaches

The child adds 9 + n by moving one counter from the second addend to complete the ten.

  • 9 only needs 1 more to make ten.
  • Take that 1 from the other number.
  • Then it is ten and some more.

Warm-Up Review

From earlier lessons. Loosen up before the new work.

4 problems

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

    Answer 15

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

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

    Answer 19

    Why 19 comes after 18.

  3. Review — One More, One Less to Twenty: One more than 11?

    Answer 12

    Why One more than 11 is 12.

  4. Review — Breaking Teen Numbers Apart: 12 is 10 and what?

    Answer 2

    Why 12 is 10 and 2.

Warm Up

Straightforward practice. Get the method working first.

3 problems

  1. 9 + 5 = ?

    Answer 14

    Why 9 + 5 = 10 + 4 = 14.

  2. 9 + 8 = ?

    Answer 17

    Why 9 + 8 = 10 + 7 = 17.

  3. 9 + 3 = ?

    Answer 12

    Why 10 + 2.

Build It Up

The same ideas with more to keep track of.

1 problem

  1. 9 + 7 = ?

    Answer 16

    Why 10 + 6.

Stretch Yourself

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

2 problems

  1. 9 + 9 = ?

    Answer 18

    Why 10 + 8.

  2. Marble Jar: Mia has 9 marbles. She finds 6 more. How many now?

    Answer 15 marbles

    Why 9 + 6 = 10 + 5 = 15.