Year 2, Unit 1, Week 2, Lesson 4 Subtraction and finding a ...

Year 2, Unit 1, Week 2, Lesson 4

Subtraction and finding a difference

National Curriculum attainment target

? Recall and use addition and subtraction facts to 20 fluently

Lesson objective

? Recall and use addition and subtraction facts to 20, using number lines, and understand the term `difference'

Previous related lessons Unit 1, Week 2, Lesson 2 Prerequisites for learning Pupils need to: ?understand and record addition and subtraction facts using

the symbols +, - and = ? recall addition and subtraction facts to 10 ? be familiar with using number lines to support calculations Vocabulary subtraction, subtract, difference, minus, equals

Future related lessons Unit 2, Week 1, Lesson 1 Success criteria Pupils can: ? relate finding a difference to numbers on a number line ?interpret the word 'difference' and carry out the appropriate

calculation ? use number lines to support finding a difference

Getting Started

? Choose an activity from Number ? Addition and subtraction. ? Choose a game or activity from Fluency in Number Facts: Y1/Y2 ? Addition

and subtraction.

Te a c h

Year 2, Unit 1, Week 2

Resources

Resource 17: 0-20 number lines, laminated (one sheet per group of 6); mini whiteboard, pen and eraser (per pair)

? Say: We can think of subtraction as taking away ? we take away an amount to find out how many are left. We can use the number line to count back from the larger number. We can also think of subtraction as finding the difference between the smaller and the larger number. A number line can also help us to find the difference ? we count up from the smaller number to the larger number.

? Display: the Number Line tool. Remind the children of their use of number lines in Year 1. Explain that in this lesson, they will be using a number line to help them work out the difference between numbers to 20 as well as some subtraction.

? Say: We are going to work out the difference between seven and five. Mark 7 and 5 on the number line as you say the numbers.

? Say: We are going to start at five and count up to seven to find out the difference between the two numbers. One, two. Draw single number jumps from 5 to 6 and 6 to 7 as you count with small arrows to indicate the direction moving to the right.

? Ask: What is the difference between seven and five? (2)

? Ask: How do you know that is the difference between the two numbers? (2 is the number that we counted up/on from 5 to 7)

? Give each pair a laminated 0?20 number line from Resource 17 together with a mini whiteboard to lean on, a pen and an eraser.

? Tell the children they should write their answer on their whiteboards and ask: How would you write the calculation for finding the difference between seven and five? (7 - 5 = 2)

? Ask: What is the difference between thirteen and eight? Say: Draw on your number line to show how you would work out the answer. Ask the children to show you their work so that you can identify any children who are struggling.

? Ask: Where on the number line did you start? Point to the number 13 on the number line on screen and make a mark. Ask: Which other number did you need to mark on the number line? (8) Ask: Then what did you do? Follow the children's instructions to mark single jumps (with an arrow), starting at 8 and moving to the right until you reach the number 13. As you do, say: One, two, three, four, five.

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Unit 1: Number -- Addition and subtraction

? Ask: Now that we have made five jumps, how do we know what the difference is between thirteen and eight? (the number of jumps from eight to 13, which is five)

? Tell the children they should write their answer on their whiteboards and ask: How would you write the calculation for finding the difference between thirteen and eight? (13 - 8 = 5)

? Repeat for finding the difference between 19 and 13. ? Say: Sometimes it makes more sense to subtract the smaller number from the larger number

than find the difference. If two numbers are close together, it is easier to find the difference. If the number being taken away is small it makes sense to subtract the two numbers rather than find the difference. ? Write: 18 - 3 = on the whiteboard and ask: Would it be better to find the difference between these two numbers, by counting on from the smaller number to the larger number, or subtract the smaller number from the larger one by counting back three from eighteen? (subtract) ? Say: Show subtracting these two numbers on your number line. Check the children's work and demonstrate the correct answer on the number line. Draw three jumps counting back (to the left) from 18. Ask: What is the answer to eighteen take away three? (15) How do you know? (the number reached after three jumps) ? Write: 15 - 11 = on the whiteboard and ask: Would it be better to find the difference between these two numbers, by counting on from the smaller number to the larger number, or subtract the smaller number from the larger one by counting back eleven from fifteen? (find the difference) ? Say: Show finding the difference between these two numbers on your number line. Check the children's work and demonstrate the correct answer on the number line. Draw jumps counting on (to the right) from 11 up to 15. Ask: What is the answer to fifteen take away eleven? (4) How do you know? (the number of jumps needed to reach 15 from 11) ? Finally, emphasise the difference between subtracting (counting back where the answer is the number reached on the number line) and finding a difference (counting on where the answer is the number of jumps).

Individualised Learning

Refer to Activity 4 from the Learning activities on page 101.

Activity Book 2A: ? Page 9: 'Take away' or 'difference'

Plenary

Resources Resource 17: 0-20 number lines, laminated (per pair); mini whiteboard, pen and eraser (per pair)

? Give each pair a laminated 0?20 number line from Resource 17, mini whiteboard, pen and eraser. Say: We are going to play a subtraction or difference game. I will give you two numbers and in your pairs you must decide whether it is better to subtract one number from the other or find the difference.

? Ask: Seventeen and four - should you subtract or find the difference? Encourage the children to use their number lines to work out their answer and show their workings. Ask: What is the answer to seventeen take away four? (13)

? Ask: How did you work out the answer? (subtracted 4 from 17 by starting at 17 on the number line and counting back four)

? Repeat for other pairs of numbers up to 20, giving some pairs where finding the difference is the best option (for example, 18 and 12, 9 and 14, 17 and 14) and some pairs where subtracting is the best option.(for example, 20 and 3, 5 and 19, 13 and 4).

Homework Guide 2

Year 2, Unit 1, Week 2, Lesson 4: 'Take away' or 'difference'? Resources: 20 of the same objects

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