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Lesson · Grade 4 · Mathematics

Friendly Numbers and Compensating: 2998 + 1456

  • Grade 4
  • Mathematics
  • 1 min 30 s
  • British Columbia
  • BC4-MA-06

On an open number line, 2998 is turned into the friendly number 3000, then 3000 + 1456 = 4456, and the extra 2 is taken away to give 2998 + 1456 = 4454; this is named compensating. The answer is checked by subtracting the same way: 4454 − 3000 = 1454, then add the 2 back to get 1456, ending on the recap "Use a friendly number, then compensate".

Concept: Adding and subtracting with friendly numbers and compensating

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In one sentence

The question this lesson answers

What is 2998 plus 1456?

2998 is just 2 less than 3000.

Transcript

What the lesson says

What is 2998 plus 1456?

2998 is just 2 less than 3000.

3000 is a friendly number, so add 3000 instead.

3000 plus 1456 is 4456.

But we added 2 too many, so take 2 away.

4456 minus 2 is 4454.

So 2998 plus 1456 is 4454.

Adding 3000, then taking 2 away, is called compensating.

To check, 4454 minus 2998 should give 1456.

Take away the friendly number 3000 instead.

4454 minus 3000 is 1454.

We took away 2 too many, so add 2 back.

1454 plus 2 is 1456, so our answer is right.

Use a friendly number, then compensate for the change.

Curriculum

Where this fits

British Columbia, Grade 4

Mathematics, Number: addition and subtraction to 10 000BC4-MA-06

Previous: Close to 0, One Half or 1? Estimating Fractions with BenchmarksNext: Adding Four-Digit Numbers with Regrouping

The outcomes and strands follow the British Columbia curriculum.

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