Video: KS1-M16S • Paper 1 • Question 24

1/3 of 21 = _.

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Video Transcript

One-third of 21 equals what?

To find a third of a number, we need to divide it by three. So we need to calculate 21 divided by three. How many threes are there in 21? To find the number of threes in 21, we could start at zero and count in threes until we reach 21: three, six, nine, 12, 15, 18, 21. We needed to make seven jumps of three to reach 21. Seven times three is 21. 21 divided by three equals seven. So one-third of 21 is seven.

To divide 21 by three, we counted in threes from zero to 21. One-third of 21 is seven.

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