Add 2-digit numbers when crossing the tens boundary | Maths

Starter quiz

Which digit is missing in this equation?

'5' ✓
Which of the following is the missing addend?

21

30

31 ✓
Use the first equation to help solve the second equation.

'44' ✓
Which of the following could be the ones digits in the equation?

3 and 4 ✓

1 and 6 ✓

3 and 3
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

36 + 23 = 35 + 24 ✓

36 + 23 = 26 + 33 ✓
Find the missing addend.

'39' ✓

Exit quiz

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

'91' ✓
Which of the following is correct?

45 + 36 = 71

68 + 28 = 96 ✓

49 + 34 = 73
Find the missing whole in the bar model.

'61' ✓
Which equation is represented by this number line?

28 + 25 = ? ✓

20 + 2 + 3 = ?

28 + 22 = ?
Which of the following is the missing addend? 35 + ______ = 71

65

36 ✓

71
Find the missing addend. 38 + ______ = 63

'25' ✓

Worksheet

Loading worksheet ...

Presentation

Loading presentation ...

Video

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.