Add 2-digit numbers when crossing the tens boundary

I can add two-digit numbers when the sum crosses the tens boundary

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Year 2

Add 2-digit numbers when crossing the tens boundary

I can add two-digit numbers when the sum crosses the tens boundary

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Lesson details

Key learning points

When adding two-digit numbers that cross the tens boundary, both addends can be partitioned, then recombined.
When adding two-digit numbers that cross the tens boundary, one addend can be partitioned. This is more efficient.
A number line can be used to find a missing addend when the tens boundary is crossed.

Keywords

Partition - To split a whole up into parts; a piece or section of a whole.

Common misconception

If children partition both addends when addition involves bridging 10, they may forget to add the extra 10 made when combining the ones.

Encourage children to consider whether an addition will bridge 10 before solving and if so, partition only one addend to reduce the number of steps required, increasing efficiency.

Encourage children to notice and articulate patterns as they work so they can begin to mentally manipulate numbers and work in the most efficient way. Ensure that a focus remains on the use of efficient strategies to avoid children defaulting to counting in ones.

Teacher tip

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).