New

New

Year 2

# Add 2-digit numbers when crossing the tens boundary

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

New

New

Year 2

# Add 2-digit numbers when crossing the tens boundary

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

## 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.

### 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.

### Keywords

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

### 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).

## Video

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## Starter quiz

Download starter quiz

### 6 Questions

Q1.

Which digit is missing in this equation?

Q2.

Which of the following is the missing addend?

21

30

Q3.

Use the first equation to help solve the second equation.

Q4.

Which of the following could be the ones digits in the equation?

3 and 3

Q5.

One of the Base 10 blocks has been moved over from one addend to the other. Which of the following could show the new equation? Tick two.

36 + 23 = 37 + 24

Q6.

Find the missing addend.

## Exit quiz

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### 6 Questions

Q1.

Partition both addends to solve the equation. 57 + 34 =

Q2.

Which of the following is correct?

45 + 36 = 71

49 + 34 = 73

Q3.

Find the missing whole in the bar model.

Q4.

Which equation is represented by this number line?

20 + 2 + 3 = ?

28 + 22 = ?

Q5.

Which of the following is the missing addend? 35 + = 71

65

71

Q6.

Find the missing addend. 38 + = 63