Number Operations (Addition… · B1 Mathematics

Lesson notes

Learning Objectives

Indicator: B1.1.2.4.1 - Use counting on, counting down and missing addend strategies for adding and subtracting within 20

By the end of the lesson, learners can:

Use counting on to solve addition facts within 20 (for example, 5 + 3 by starting at 5 and counting 6, 7, 8).
Use counting down to solve subtraction facts within 20 (for example, 15 - 3 by starting at 15 and counting 14, 13, 12).
Apply the missing addend strategy to solve subtraction facts within 20 by rewriting them as addition sentences (for example, 7 - 2 = 5 because 5 + 2 = 7).
Explain which strategy they used to solve an addition or subtraction fact and justify why their answer is correct.
Solve simple word problems within 20 by choosing and applying an appropriate strategy.

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Curriculum details

Strand: Number (Strand 1)
Sub-strand: Number Operations (Addition, Subtraction, Multiplication and Division) (1.2)
Content standard: B1.1.2.4 - Apply strategies for adding and subtracting to 20
Indicator: B1.1.2.4.1 - Use counting on, counting down and missing addend strategies for adding and subtracting within 20
Suggested placement: Term 2, Week 5 (Week 17 of the year)
Our suggestion, laid out in curriculum order across three terms of twelve weeks. NaCCA does not fix the week, so follow your school's scheme of learning.
Curriculum reference: Mathematics Curriculum for Primary Schools (Basic 1-3), 2019, p. 9
Transcribed from the official NaCCA publication. Check this page against the source.

Exemplars (from the NaCCA curriculum)

E.g. 1. Relating counting to addition (i.e., recognizing that adding 2 is the same as counting on 2)
E.g. 2. Counting on (i.e., for 5 + 3, start at 5 and count on 3 places... 6, 7, 8. The answer is 8.)
E.g. 3. "Making 10s" (i.e., if 7 + 2 + 3, do 7 + 3 = 10 first then add 2. The answer is 12. Or if given 7 + 2 + 3, change the order of the addends to 7 + 3 + 2 to produce combinations that add to 10; Or if given 2 + 6 + 4, add the two last addends first to produce 2 + 6 + 4 = 2 + 10 = 12 Or if given 8 + 3, change question to 8 + 2 + 1 = 10 + 1 = 11)
E.g. 4. "Making doubles" (i.e., if 5 + 4, do 4 + 4 = 8 then add 1. The answer is 9. Or if given 6 + 7, change question to 6 + 6, which give 12 then add 1. The answer is 13).
Relating subtraction to counting down (i.e., Recognizing that subtracting 3 is the same as counting down 3) (i.e., for 15 - 3, start at 15 and count on 3 places... 14, 13, 12. The answer is 12.)
E.g. 5. Relating subtraction to comparison or finding the difference (Recognizing that subtracting 5 from 8 is the same as ' 5 is how many less than 8; or '8 is how many more than 5;
E.g. 6. "Using addition to subtract" or re-writing as addition sentence and finding the missing addend (i.e., if given 7 - __ = 5, change the question to the addition 5 + ___ = 7. The answer is 2, so 7 - 2 = 5.
7 - What? = 5 means 5 + What? = 7
Or if given 8 - 6 = ___ change question to 6 +__ = 8. The answer is 2, so 8 - 6 = 2). That is,
8 - 6 = What? means 6 + What? = 8