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Lesson · Grade 3 · Mathematics

Friendly Numbers: Estimate First, Then Adjust

  • Grade 3
  • Mathematics
  • 1 min 22 s
  • British Columbia
  • BC3-MA-09

To work out 298 + 145, the video rounds 298 up to the friendly number 300, estimates 300 + 145 = 445, then takes away the extra 2 to get 443, shown step by step on a number line. It then does the same for 523 − 198 (take away 200 to get 323, then add the 2 back for 325) and ends with the recap "Estimate first, then adjust."

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In one sentence

The question this lesson answers

What is 298 plus 145?

298 is very close to 300.

Transcript

What the lesson says

What is 298 plus 145?

298 is very close to 300.

300 is a friendly number, just 2 more than 298.

Add the friendly number first: 300 plus 145 is 445.

But we added 2 too many.

So adjust by taking the 2 away.

445 minus 2 is 443.

So 298 plus 145 is 443.

It works for subtraction too, like 523 minus 198.

198 is close to 200, so take away 200 first.

523 minus 200 is 323.

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

323 plus 2 is 325.

So 523 minus 198 is 325.

Use a friendly number first, then adjust.

Curriculum

Where this fits

British Columbia, Grade 3

Mathematics, Number: addition and subtraction to 1000BC3-MA-09

Previous: Subtracting Three-Digit Numbers: Trade a Ten for Ten OnesNext: Make a Ten to Add

The outcomes and strands follow the British Columbia curriculum.

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