Year 3 Teaching Sequence Spring 11 - Multiplication and division (including commutativity and finding remainders) (four days) Prerequisites: Know by heart multiplication facts for 2, 3, 5, and 10 times tables (see oral and mental starter banks 10 and 11) Begin to know by heart multiplication facts for the 4 times table (see teaching sequence 10 and oral and mental starter bank 11) Multiply single-digit numbers by 2, 3, 4, 5 and 10, and divide two-digit numbers by the same (answers not greater than 10) (see autumn teaching sequence 11) Understand how multiplication is commutative (see autumn teaching sequence 11 and spring oral and mental starter bank 11) Understand that division can leave a remainder (initially as ‘some left over’) (see autumn teaching sequence 11) Overview of progression: Children revise the concept of commutativity (a x b b x a) and use this to solve multiplication of single-digit numbers choosing which order will help them to make use of their multiplication facts, or make the counting on easier. Children use division and their knowledge of multiplication facts to find mystery numbers in multiplication and division sentences. They use grouping to divide numbers by 2, 3, 4, 5, 9 and 10 including those which leave a remainder and make up their own divisions which leave a remainder of 1. Remainders are discussed in the context of word problems. Note that multiplication sentences can be read in two ways; 4 × 5 can be read as four fives (4 lots of 5) or alternatively as 4 multiplied by 5, i.e. 4, five times (5 lots of 4). Children need to be aware of the different terminology used (lots of, times, multiplied by), but more importantly understand that multiplication is commutative and so the answer is the same whichever way round we write a multiplication. Thus 4 lots of 5 is equivalent to 5 lots of 4. Understanding commutativity helps children to multiply efficiently. Note that the grouping model of division is used in this sequence to relate multiplication and division. There is a more natural link between grouping and multiplication facts (e.g. four 10s are 40, how many 10s in 40?) that between sharing and multiplication. For this reason it is important that the ÷ sign is not read as ‘sharing’, which would confuse the two models. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y3 Maths TS11 – Spr – 4days Watch out for children who try to share between groups rather than using grouping, as once learnt this will be easier to visualise and more efficient when dividing larger numbers too cumbersome to share. Watch out for children who do not understand the link between multiplication and division, and so cannot use one to solve the other, particularly in missing number problems. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y3 Maths TS11 – Spr – 4days Objectives: Understand the vocabulary ‘multiplied by’ and the concept of commutativity Multiply single digits by 2, 3, 4, 5, 9 and 10 Divide two-digit numbers by 2, 3, 4, 5, 9 and 10 (answers not greater than 10, but including remainders) Begin to decide whether to round up or down after division depending on the context Whole class Group activities Paired/indiv practice Resources Write 3 × 6 on the board. Explain that this can be read as ‘three lots of six’, or ‘three multiplied by six’. Which way would you work this one out? Three lots of six or six lots of three? We haven’t learned our sixes yet so perhaps six lots of three might be easier! Draw six jumps of three above a 0-100 beaded line and three jumps of six below it, to show that they come to the same number. What divisions could we write to go with these hops? Write 18 ÷ 3 = 6 above the line to go with the six hops of three, and 18 ÷ 6 = 3 below the line. Also show an array of six rows of three: Group of 4-5 children Write 5 × 4 on the flipchart. What pictures could we draw to go with this multiplication? Sketch them on your whiteboards. Share children's sketches and agree that we could draw an array or hops on a number line. What are five 4s? And four 5s? What pictures show each of these? Draw the pairs of arrays and number line jottings on the flipchart. Write the complete multiplications on the flipchart by the side of the relevant number line jotting. If we know five 4s are 20, what division can we write? What number line jotting goes with this? What division can we write to go with the other number line jotting? Repeat with 4 × 6. Easier: Use 3 × 4 and 2 × 10. Harder: Use 4 × 6, and then ask children to work in pairs to choose their own multiplication and to write the other three related multiplication and division facts. Share children’s responses. Write the following multiplications on the board: 10 × 5, 2 × 8, 3 × 4, 7 × 2, 5 × 7, 4 × 6, 4 × 10, 7 × 9, 9 × 5, 8 × 4. Children work through them to practise multiplying single digits together. They write how they decided to find the answer, so for example for 5 × 7 they write 7 lots of 5 if they choose to count on in 5s or use their tables facts for 5 rather than counting on in 7s. Children use a 0-100 beaded line (see resources) to help them with any for which they don’t yet know the multiplication facts (particularly multiples of 9). Easier: Children will probably need to use a 0-100 beaded line to support counting on more frequently. Harder: Ask children to write the division sentence to go with the way they solved the multiplication, e.g. if they worked out 4 × 6 by working out six fours, they record 24 ÷ 4 = 6. Large 0100 beaded line 0-100 beaded lines (see resources) Discuss how we can find the total by counting in threes down the rows, or else in sixes across the columns. Rotate the array to show three rows of six, and discuss how we can count in threes or sixes to find the same total. Write 6 × 9. How can we read this? We don’t yet know our 6 or 9 times table, would you prefer to count on in 6s or 9s? Count along the 100 bead bar slowly in sixes, and then in nines. Discuss that adding nine on each time is actually quite easy as we can think of adding ten, and © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Y3 Maths TS11 – Spr – 4days then subtract one. Count in nines to 99 along the bead bar to practise this. Also show recording hops of 6 and 9 above and below the 0-100 beaded line to help children see that the answer is the same. What division sentences could we write? Write 5 × 6 = 30 on a card, and use a ‘slidy box’ to cover up the 6. 5 × - = 30 What number do you think might be hiding? Why do you think that? We could read this as five lots of something equals thirty, or five multiplied by something equals thirty. How many fives are in thirty? What division number sentence could we write? Reveal the mystery number. Show the following: 20 ÷ 5 = 4 What number do you think is hiding? Why do you think that? We can read this as something divided into groups of five, gives four groups. What are four 5s? What multiplication sentence could we write? Reveal the mystery number. Repeat with slidy box cards for other multiplication facts e.g. 3 × = 18, × 4 = 24, ÷ 5 = 3, ÷ 3 = 4, ÷ 4 = 3. Group of 4-5 children Write the following number story on the flipchart: There are children. They get into groups of . There are groups. Ask children to discuss what numbers could go in this story to make it true. Which will be the biggest number? Why do you think that? What size groups might they get in? What multiplication facts could we use to help us? Take feedback, and try out children's suggestions. Write them on Post-its™, put them in the story and discuss if they make sense. What other numbers could we put in this story? Repeat for the following story: Matthew has coins. They are all p pieces. Altogether he has p. Easier: You may need to make a sketch to show if children’s ideas work, for example sketching four groups of 5 smiley faces to show 20 children altogether. Harder: Say that one number must be greater than 20. Children work in pairs to each fill in the missing numbers in multiplication and division sentences (see resources). Encourage them to use multiplication to check their answers, counting in fours, for example, on their fingers if they don’t know the appropriate multiplication fact. Easier: Children use 0-100 beaded lines to help them to work out the mystery multiplications. Harder: Ask children to also write division sentences to go with at least four of the multiplications. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Slidy box cards as opposite Post-its™ Activity sheet of multiplicati on and division sentences with missing numbers (see resources) Y3 Maths TS11 – Spr – 4days Write 17 ÷ 5 on the board. What does this mean? Read it both as ‘seventeen divided by five’, and ‘how many fives in seventeen?’ How many fives do you think there might be in 17? Do you think there will be a remainder? Why? Launch the ITP Grouping, and choose 17 ÷ 5 as the calculation. Click on 17 to show 17 objects, and then click on five to show one group. Can we make another five? Repeat clicking on fives until there are only two left. What's happened? Click to show the number sentence. The little ‘r’ stands for remainder, the number left over. What do you think would happen if we had 16 divided by 5? Draw three hops of five on a large 0-100 beaded line, and point out the one left over. What if we had 18 ÷ 5, how many would be left then? Write the division on your whiteboards. And 19 ÷ 5? And what happens when we have 20 ÷ 5? Discuss how we have an extra one, and so we can make another group of five. Group of 4-5 children Write the following word problem on the flipchart: Jess has 17 stickers. She puts five stickers on each page of her sticker album. How many pages can she fill? Ask children to discuss this. What do we need to do to solve it? Agree that we need to find out how many 5s there are in 17 as this will tell us how many pages she will fill. We found that there are three fives in 17, and two left over. So what’s the answer to the number story? Agree that the answer to the question is three. What do you think Jess will do with the other two? Write the following number story on the flipchart: Jess has 17 stickers. She puts five stickers on each page of her sticker album. How many pages will she need to put them all in her album? Ask children to discuss this problem. What do we need to work out this time? We know 17 divided into groups of five is three and 2 left over. So how many pages will she need? So the answer to this problem is four! Repeat with similar word problems, discussing the necessary divisions, but then how this is not necessarily the Write the following divisions on the board: 32 ÷ 5, 13 ÷ 2, 14 ÷ 4, 33 ÷ 10, 20 ÷ 9, 22 ÷ 3, 51 ÷ 5, 45 ÷ 10, 25 ÷ 4, 17 ÷ 3. Children work through them to practise dividing by 2, 3, 4, 5, 9 and 10. Children use a 0-100 beaded line (see resources) to help them with any for which they don’t yet know the multiplication facts (particularly multiples of 9). Easier: Children will probably need to use a 0-100 beaded line to support counting on more frequently. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Large 0100 beaded line 0-100 beaded lines (see resources) Y3 Maths TS11 – Spr – 4days Write the following numbers on the board: 21, 25, 13, 26 and 31. Which of these numbers do you think would have a remainder of 1 when divided by 10? Why? Take children’s suggestions and test them out by drawing hops on the 0100 beaded line. Work with a partner to come up with another division by 10 that will give a remainder of 1. Which do you think will have a remainder of 1 when divided by 5? Take children’s suggestions and test them out by drawing hops on the 0-100 beaded line. And by 3? And by 4? Test out chn’s suggestions. answer to the ‘real-life’ problem. Easier: You may need to represent the objects in the stories with cubes to ensure children's understanding of what to do with the objects in the story. Group of 4-5 children What remainders do you think are possible when dividing by 5? Ask chn to work in pairs to divide numbers 10 to 20 by 5 and discuss what they find. When you divide by 5, could you get a remainder of 6? Why not? Agree that there would be another group of five. What remainders do you think you can get when dividing by 4? Take chn’s suggestions and ask them to try them out by dividing numbers 10 to 20 by 4. Easier: Discuss what remainders are possible when dividing by 2, then 5, using counters to show the remainders. Ask chn to make up ten of their own divisions that would give a remainder of 1. Easier: Children will probably need to use a 0-100 beaded line. Suggest that they only divide by 10 and 5. Harder: Children think of divisions that will give a remainder of 2. © Original teaching sequence copyright Hamilton Trust, who give permission for it to be adapted as wished by individual users. Large 0100 beaded line 0-100 beaded lines (see resources) Y3 Maths TS11 – Spr – 4days