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Lesson · Grade 7 · Mathematics

Subtracting integers: add the opposite

  • Grade 7
  • Mathematics
  • 1 min 1 s
  • British Columbia
  • BC7-MA-10

The video works out 9 − (−4) by changing the subtraction to an addition, then using a number line to show that the opposite of −4 is 4, the same distance from zero on the other side. That turns the question into 9 + 4, which is 4 steps right of 9 on a number line, landing on 13, and it ends on the recap: to subtract an integer, add its opposite.

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In one sentence

The question this lesson answers

What is 9 minus negative 4?

Subtracting an integer is the same as adding its opposite.

Transcript

What the lesson says

What is 9 minus negative 4?

Subtracting an integer is the same as adding its opposite.

First, change the subtraction into an addition.

Next, find the opposite of negative 4.

Negative 4 is 4 steps to the left of zero.

Its opposite is the same distance on the other side, which is 4.

So change negative 4 into its opposite, 4.

Now 9 minus negative 4 is the same as 9 plus 4.

On a number line, start at 9.

Adding 4 means taking 4 steps to the right.

We land on 13, so 9 plus 4 is 13.

So 9 minus negative 4 equals 13.

Remember: to subtract an integer, add its opposite.

Curriculum

Where this fits

British Columbia, Grade 7

Mathematics, Number: operations with integersBC7-MA-10

Previous: Adding Integers with Counters and Zero PairsNext: Multiplying integers: the sign rules

The outcomes and strands follow the British Columbia curriculum.

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