Use number facts to add or subtract a one-digit number and a two-digit number. | Maths

Starter quiz

Which decade is missing on the number line?

the fifties

the sixties

the forties ✓
Alex subtracts 1 from these Base 10 blocks. Which image shows the number he now has?
Alex taps one more than the number shown. What number does he tap?

'70' ✓
Which number is missing?

'90' ✓
Which of the following could be Sam’s number?

40 ✓

38

70 ✓
Alex thinks of a two-digit number. It is 1 less than a multiple of ten. It is greater than 80 but less than 90 What is his number?

'89' ✓

Exit quiz

Which equation would come next in the pattern?

2 + 7 = 9

12 + 7 = 19

22 + 7 = 29

32 + 7 = 39 ✓

42 + 7 = 49
Which known fact could be used to solve the equation shown on the number line?

4 + 3 = 7 ✓

4 - 1 = 3

3 + 4 = 7 ✓

5 + 5 = 10
Which of the following equations can be solved using the known fact 3 + 5 = 8?

45 + 3 = ✓

58 + 3 =

63 + 5 = ✓
Which number will make both of the following equations correct?

'5' ✓
Match the missing number equations to the correct answer.

49 = ___ + 46

⇔

3 ✓

___ + 6 = 49

⇔

43 ✓

49 − ___ = 43

⇔

6 ✓
What number did Alex add?

'4' ✓

Worksheet

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Lesson Details

Key learning points

Known facts can be used to help solve equations with larger numbers.
Partitioning a two-digit number into tens and ones can help with seeing the pattern in the ones.
When adding to or subtracting from the ones without crossing the tens boundary, the tens digit does not change.

Common misconception

Children may not recognise known facts when addends are presented in different order, e.g. they may not use 7+1 to solve 61 +7 They may also confuse tens and ones digits.

Focus on efficient ways of working and, when working in the abstract, partition the two-digit number into tens and ones, so the tens and ones digits can be easily identified and the commutative aspect of the ones digit can be more easily seen.

Keywords

Equation - An equation has an equal sign. It shows that what is on the left of the equation is equal to what is on the right.