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The answer key. Print this one for yourself, not for the child.

Cogito

Grade 2 Math · Chapter 1 · Lesson 3

Answer Key

Make Ten to Add

Get to ten first, then add what is left.

10 problems · about 12 minutes · 2.OA.B.2

What this lesson teaches

The child adds within 20 by making ten, and chooses which addend to complete.

  • Ten and some more is the easiest sum to say.
  • Fill one number up to ten, then add what is left.
  • Fill whichever number is closer to ten.

Warm-Up Review

From earlier lessons. Loosen up before the new work.

2 problems

  1. Review — Near Doubles: 8 + 9 = ?

    Answer 17

    Why 8 + 8 = 16, and one more makes 17.

  2. Review — Doubles: 7 + 7 = ?

    Answer 14

    Why 7 + 7 = 14.

Warm Up

Straightforward practice. Get the method working first.

4 problems

  1. 9 + 8 = ?

    Answer 17

    Why 9 + 1 + 7 = 10 + 7 = 17.

  2. In 7 + 8, which number is easier to fill to ten?

    Answer The 8. It only needs 2.

    Why The 8 is closer, so it needs less taken from the other number.

  3. 9 + 4 = ?

    Answer 13

    Why 9 needs 1.

  4. 8 + 7 = ?

    Answer 15

    Why 8 needs 2.

Build It Up

The same ideas with more to keep track of.

2 problems

  1. 7 + 6 = ?

    Answer 13

    Why 7 needs 3.

  2. 5 + 9 = ?

    Answer 14

    Why Fill the 9. It only needs 1.

Stretch Yourself

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

2 problems

  1. Fruit Bowl: There are 9 apples and 7 oranges in a bowl. How many pieces of fruit are there?

    Answer 16 pieces

    Why 9 + 1 + 6 = 10 + 6 = 16.

  2. Reading Time: Leo read 8 pages before lunch and 6 after. How many pages did he read?

    Answer 14 pages

    Why 8 + 2 + 4 = 10 + 4 = 14.