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Lesson · Grade 5 · Mathematics

Multiply by 5: Times 10, Then Halve

  • Grade 5
  • Mathematics
  • 1 min 16 s
  • British Columbia
  • BC5-MA-18

The video works out 214 × 5 by first showing that 5 is half of 10, then multiplying 214 by 10 on a place value chart to get 2140. It halves 2140 in easy parts (2000 and 140) to reach 1070, checks this with the estimate 200 × 5 = 1000, and ends on the recap "Multiply by 5: times 10, then halve."

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In one sentence

The question this lesson answers

What is 214 times 5?

Here is the trick: 5 is half of 10.

Transcript

What the lesson says

What is 214 times 5?

Here is the trick: 5 is half of 10.

So multiplying by 5 is the same as multiplying by 10, then halving.

Step 1: multiply 214 by 10.

Each digit moves one place to the left, and a zero fills the ones place.

So 214 times 10 is 2140.

Step 2: find half of 2140.

Split 2140 into 2000 and 140, which are easy to halve.

Half of 2000 is 1000.

Half of 140 is 70.

Put the halves together: 1000 plus 70 is 1070.

So 214 times 5 is 1070.

Check: 200 times 5 is 1000, so 1070 is about right.

To multiply by 5, multiply by 10, then halve.

Curriculum

Where this fits

British Columbia, Grade 5

Mathematics, Number: multiplication and division facts to 100 (emerging computational fluency)BC5-MA-18

Previous: 15.2 − 7.85Next: Multiply by 4 and by 8 by doubling

British Columbia, Grade 7

Mathematics, Number: multiplication and division facts to 100BC7-MA-01

Next: Multiply by 4 and by 8 by doubling

This lesson is also listed in Grade 7.

The outcomes and strands follow the British Columbia curriculum.

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