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Lesson · Grade 3 · Mathematics

Fact families: adding and subtracting are related

  • Grade 3
  • Mathematics
  • 1 min 18 s
  • British Columbia
  • BC3-MA-12

A row of 3 red and 9 yellow counters builds the fact family 3 + 9 = 12, 9 + 3 = 12, 12 − 9 = 3 and 12 − 3 = 9, and taking counters away checks both subtractions. Thinking "9 plus what makes 12?" solves 12 − 9, and the video ends on the recap: to subtract, think addition.

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In one sentence

The question this lesson answers

What is 12 minus 9?

Here are 3 red counters and 9 yellow counters.

Transcript

What the lesson says

What is 12 minus 9?

Here are 3 red counters and 9 yellow counters.

Together, there are 12 counters.

So 3 plus 9 equals 12.

Swap the groups, and 9 plus 3 still equals 12.

To find 12 minus 9, think: 9 plus what makes 12?

9 plus 3 equals 12, so 12 minus 9 equals 3.

Check with the counters: take away the 9 yellow ones.

3 red counters are left, just as we found.

Take away the 3 red ones instead: 12 minus 3 equals 9.

These four facts make a fact family.

They all use the same three numbers: 3, 9 and 12.

To subtract, think addition: 9 plus 3 is 12, so 12 minus 9 is 3.

Curriculum

Where this fits

British Columbia, Grade 3

Mathematics, Number: addition and subtraction facts to 20 (emerging computational fluency)BC3-MA-12

Previous: Doubles and Near Doubles: 6 + 7Next: Multiplying means equal groups

The outcomes and strands follow the British Columbia curriculum.

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