Combine tens and ones within equations | Maths | Quizalize & Oak National Academy

Starter quiz

Andeep wants to solve the equation 2 + 40 + 50 = ? Which is the most efficient strategy to use?

use a known fact ✓

bridge 10

think of a Gattegno chart
Andeep estimates the cost of the items shown. Which of the following is most likely to be accurate?

The sum will be in the twenties.

The sum will be in the thirties ✓

The sum will be in the forties.
For which of the following equations would you use the bridge 10 strategy?

34 + 20 = ?

34 + 2 = ?

34 + 7 = ? ✓
For which equations would you use the known facts strategy? Tick two.

64 + 30 = ? ✓

64 + 3 = ? ✓

64 + 8 = ?
Andeep’s items cost £54 Which of the following will be the cost of Izzy’s items?

£55

£56

£53 ✓
Match to show which equations will have the same sum.

36 + 7 =

⇔

37 + 6 = ✓

32 + 9 =

⇔

39 + 2 = ✓

35 + 3 =

⇔

33 + 5 = ✓

Exit quiz

Use the Base 10 blocks shown to solve the equation.

'69' ✓
Match the expressions which have the same value.

40 + 1 + 3 + 20

⇔

1 + 40 + 3 + 20 ✓

30 + 1 + 20 + 4

⇔

4 + 1 + 30 + 20 ✓

10 + 2 + 30 + 4

⇔

2 + 10 + 30 + 4 ✓
What is the missing whole in the bar model?

98

89 ✓

69
Tick the correct equation.

4 + 50 + 2 + 20 = 67

20 + 4 + 2 + 50 = 67

5 + 20 + 40 + 2 = 67 ✓
Match the equations to the correct missing addend.

7 + 1 + ___ + 20 = 68

⇔

40 ✓

30 + 2 + ___ + 5 = 57

⇔

20 ✓

20 + 40 + ___ + 2 = 65

⇔

3 ✓
Which of the digit cards shown would complete the equation?

2 and 3 ✓

3 and 4

4 and 5

Worksheet

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Presentation

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Video

Lesson Details

Key learning points

Known strategies can be used to help us prepare for the addition of two 2-digit numbers.
It is important to be able to calculate mentally before adding two 2-digit numbers.

Common misconception

Children may rely on the order of the addends rather than their place value when calculating. They may also default to counting on rather than using known facts.

Refer back to known facts and efficient strategies and model their use throughout, discussing the best strategy to use at each point and why. Model errors that can be made when not adding ones then tens for example, or in counting on in ones.

Keywords

Calculate - To work out an answer, often by adding or subtracting.
Efficiently - Not wasting time or effort. An efficient strategy is one we can carry out easily.