Use efficient addition strategies to calculate | Maths

Starter quiz

Look at the items in the shop. How much would a ball and a car cost? £______

'7' ✓
Izzy buys an astronaut and a rocket. Which known fact would she use to help her calculate the cost?

3 + 4

4 + 5 ✓

3 + 5
Andeep spent £43 at the shop. Which two items did he buy?

the ball and the astronaut ✓

the rocket and the ball

the astronaut and the car
Which known fact would you use to calculate the cost of a penguin and an astronaut?

4 + 2 = 6

4 + 4 = 8 ✓

42 + 4
Which known fact would you use to calculate the cost of a unicorn and a car?

4 + 4 = 8 ✓

6 + 4 = 10

64 + 4 = 68
Andeep uses the 'bridge 10' strategy to find the cost of two items. Which two items were they?

the gloves and the trainers

the socks and the t-shirt

the sunglasses and the trainers ✓

Exit quiz

Izzy wants to solve the equation 2 + 4 + 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 cost will be in the forties. ✓

The cost will be in the fifties.

The cost will be in the sixties.
For which of the following equation, would you use the bridge 10 strategy?

45 + 3 = ?

45 + 4 = ?

45 + 8 = ? ✓
For which equations would you use the known facts strategy? Tick two.

42 + 9 = ?

42 + 30 = ? ✓

42 + 3 = ? ✓
Andeep’s items cost £35 Which of the following shows the cost of Izzy’s items?

£34

£36 ✓

£35
Match to show which equations will have the same sum.

44 + 6 =

⇔

46 + 4 = ✓

47 + 5 =

⇔

45 + 7 = ✓

42 + 3 =

⇔

43 + 2 = ✓

Worksheet

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Lesson Details

Key learning points

We can use strategies we already know 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 not be able to mentally calculate or identify efficient strategies and so revert to counting on in ones.

Assess use of mental strategies before starting this lesson as it is important to be fluent in using strategies with smaller numbers before working with larger numbers to avoid reverting to inefficient counting strategies.

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.