Year 5, Unit 1, Week 2, Lesson 1 Adding mentally - Collins

Year 5, Unit 1, Week 2, Lesson 1

Adding mentally

National Curriculum attainment target

? Add numbers mentally with increasingly large numbers

Previous related lessons none

Prerequisites for learning Pupils need to: ? understand the place value of numbers up to 10 000 ? begin to understand the place value of numbers up

to 100 000 ? add mentally four-digit numbers and hundreds, tens

and ones Vocabulary ten thousands, thousands, hundreds, tens, ones, add

Lesson objective

? Add numbers mentally

Future related lessons Unit 3, Week 1, Lesson 1; Unit 9, Week 2, Lesson 1; Unit 11, Week 1, Lesson 1 Success criteria Pupils can: ? know which digits to focus on ? add mentally using the number line or jottings

Getting Started

? Choose an activity from Number - Addition and subtraction. ? Choose a game or activity from Fluency in Number Facts: Y5/Y6 ? Addition and subtraction.

1

Add on in individual jumps of hundreds or tens, for example, add four hundred in jumps of one hundred.

Te a c h

Resources mini whiteboard, pen and eraser (per child)

Year 5, Unit 1, Week 2

? Display: Slide 1 and say: These are the kinds of addition calculations that you worked out mentally in Year 4.

? Say: Discuss how to work out these calculations mentally.

? Ask: Which calculation are you most confident adding mentally? Underline the calculation that most children felt confident with.

? Ask: Which calculation are you least confident adding mentally? Circle the calculation that most children felt least confident with.

? Ask some pairs to share their reasons for their choices. Draw out the aspects of the calculation that children found tricky.

? Model the calculation the class felt the least confident with using an empty number line. Add the most significant digits first.

? Emphasise which digits change and which digits stay the same each time you make a jump on the number line, for example, when the 400 from 450 is added to 1260, only the hundreds digit changes, the other digits remain the same.

? Say: The empty number line supports our mental strategies. If you can add mentally in your head, then you do not need to use the empty number line. You could use jottings instead of the empty number line.

? Model the use of jottings for the calculation you have just worked out.

? Work through any of the other calculations with the class, if appropriate.

? Write two or three calculations of the same type as the ones you have worked through as a class on the board.

? Say: Work these calculations out mentally, showing your working out on your whiteboard.

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Unit 1: Number - Addition and subtraction

2

Change the calculations to 24 712 + 80, 24 362 + 500, so the thousands and hundreds boundaries are not crossed.

3

? Display: Slide 2 and say: We can use our mental addition skills for five-digit numbers.

? Ask: When 80 is added to 24 762, which digits will change and which will stay the same? Establish that, as the hundred boundary will be crossed, the tens and the hundreds digits will change.

? Work through the calculation as a class using the empty number line, if appropriate.

? Ask: When 500 is added to 24 762, which digits will change and which will stay the same? Establish that, as the thousand boundary will be crossed, the hundreds and the thousands digits will change.

? Work through the calculation as a class using the empty number line, if appropriate.

? Ask: When 4000 is added to 24 762, which digits will change and which will stay the same? Establish that, as no boundaries will be crossed, only the thousands digit will change.

? Work through the calculation as a class using the empty number line, if appropriate.

? Display: Slide 3 and say: Work out these calculations mentally.

? Check children's answers and work through the calculations, if appropriate.

Individualised Learning

Refer to Activity 1 from the Learning activities on page 90.

Pupil Book 5A: ? Page 12: Adding mentally

Progress Guide 5: ? Support, Year 5, Unit 1, Week 2, Lesson 1: Using the number line

Plenary

? Write 25 871 + 13 000 on the board. ? Ask: How would you work this out mentally? ? Ask some pairs to share their ideas. ? Establish that, as ten thousands are being added, then the mental calculation that needs

to be done is 25 000 add 13 000. Write this on the board. ? Say: Work this out mentally. Ask someone to share their strategy. ? Ask: What is the answer to our original calculation? ? Say: Explain why the hundreds, tens and ones digits stay the same. Ask a pair to share

their explanation. ? Ask the rest of the class to comment on and improve the explanation.

Overcoming Barriers

? Children will find adding mentally with these large numbers challenging if they are not very confident with the place value of four- and five-digit numbers. Ensure they add in jumps of ten, one hundred or one thousand as this will provide them with counting practice as they carry out the calculation.

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