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Using Near Doubles: What is it?
'Using near doubles' is an addition and subtraction strategy. Students use their knowledge of double facts (eg. 4+4) to help solve the equation. The doubles strategy is helpful in addition/subtraction and important to begin preparing students for multiplicative reasoning.
Overview:
Doubles are facts that have two addends that are the same. By familiarizing themselves with the doubles facts, students can efficiently use them to solve near-doubles problems. Near-doubles are facts that have one added that is one more than the other addend. Students need to be comfortable with their doubles before they can attempt to use this strategy effectively. Doubles and near doubles appear in the Addition & Subtraction continuum. Doubling, a similar strategy, can be found on the multiplication/division continuum.
Supporting Students 'Using Near Doubles'
To ensure students grasp what is happening when they double, have them build the amount with a concrete item, like snap cubes, and then double it. Students can also be encouraged to learn double facts for higher numbers (eg. 21 + 21) Once students have automatic recall of their doubles facts they will be able to transfer this to solving questions with near doubles.
When students are comfortable with their doubles facts, this will also support their understanding of multiplication tables. For example, the two times tables (doubling 2’s) can then use these facts for the three times tables. For example, if 2x4 is 8, then 3x4 is 8 plus one more 4.
Where to Next?
Once students are confident with using near doubles, they can be encouraged to move towards 'Taking jumps of 10 forward or backward' or 'Splitting'.
Games & Activities to Support 'Using Near Doubles'
Number Strings
Number Strings
In the Lawson text, What To Look For, there is a sample number sequence (string) for whole class or small groups around the doubles/near doubles strategy (Lawson; pg. 199).
Snappy Doubles
Snappy Doubles
In this fast-paced partner game, students race to 'snap' their double before their opponent. (GEIM; volume 5, pg. 75 print or pg. 81 PDF)
http://www.eworkshop.on.ca/edu/resources/guides/guide_math_k_6_volume_5.pdf
Last One to School
Last One to School
Players race against one another to empty their houses, getting all of the students to school. This game focuses on doubles using a spinner or standard die. (GEIM; volume 5, BLM 11 or pg. 97 PDF)
http://www.eworkshop.on.ca/edu/resources/guides/guide_math_k_6_volume_5.pdf
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