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How to use approximation and rounding to get rough answers for two-digit subtractions. A dance routine and song show children finding rough answers for two-digit subtractions, using rounding to the nearest 10 to approximate numbers before they are added. The calculations illustrated are 41-18 and 62-29.
This clip is from:
First broadcast:
26 November 2001

Classroom Ideas

As children watch the clip, ask them to note down the two questions that are asked. Ask children what is the same and what is different about the two calculations (the amount that is subtracted is close to a multiple of 10). Play the more/ less game. Each child makes a card with 'more' on the front and 'less' on the back. They are then asked a series of questions and have to show their card to indicate if the answer is more or less than an amount eg 56 -19 – will this be more or less than 36? 42 – 18 – will this be more or less than 20? They can be awarded points for correct answers and answers to the question "how did you know?"