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Arithmetic: Mental Calculation

PGCE. Arithmetic: Mental Calculation. Learning Objectives:. Be familiar with the models of the four operations Be aware of the properties of the four operations Be aware of the relevant vocabulary Become familiar with a range of mental strategies

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Arithmetic: Mental Calculation

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  1. PGCE Arithmetic: Mental Calculation

  2. Learning Objectives: • Be familiar with the models of the four operations • Be aware of the properties of the four operations • Be aware of the relevant vocabulary • Become familiar with a range of mental strategies • Consider the importance of structured jottings

  3. What do we mean by addition, subtraction, multiplication and division? SHOW ROSS AND HIS CUBES CLIP

  4. Understanding addition, subtraction, multiplication and division In order to be able calculate using the four operations a child needs to know: • The different models of addition, subtraction, multiplication and division • The properties of the four operations • Vocabulary

  5. Models of addition • Combining 1, 2, 3 and 1, 2 together makes 1, 2, 3, 4, 5 • Counting on 3 and 2 together makes 3, 4, 5

  6. Models of subtraction • Taking away • Counting back • Difference Can you find an example for each?

  7. The Singapore Bar MethodAddition - Aggregation There are 3 footballs in the red basket 2 footballs in the blue basket. How many footballs are there altogether?

  8. Addition - Augmentation • Peter has 3 marbles. Harry gives Peter 1 more marble. How many marbles does Peter have now? Concrete Abstract

  9. Subtraction - Comparison Model • Peter has 5 pencils and 3 erasers. How • many more pencils than erasers does he • have?

  10. Moving to the abstract • Peter has 5 pencils and 3 erasers. How many more pencils than erasers does he have?

  11. Generalisation

  12. Giving meaning to calculations Number stories for 5+3=8 Which models would you use? • I have 5 sweets and my friend gave me 3 more. How many do I have altogether? • My sister is 5 years old. How old will she be in 3 years time?

  13. Number stories for 8-3=5 Which models would you use for children? • There are 8 apples on a tree. The squirrel ate 3. How many were left? • I am 8 and my sister is 3. How many years older am I than my sister? • I have 3 conkers and my friend has 8. How many more has he got than me?

  14. What is multiplication? Repeated addition Lots of / groups of Arrays Scaling (n times as many, as long, as heavy…) Models for multiplication

  15. Models for division What is division? • Sharing (equal) • Grouping, linked to: • Repeated subtraction

  16. ITPs available to support • Arrays • Grouping & number line models

  17. Addition Subtraction Multiplication Division Vocabulary

  18. Properties 3 4 7 12 Write some number sentences using the numbers above. Use all four operations eg 3 + 4 = 7

  19. Property 1: Inverse 4 + 3 = 7 So … 7 – 3 = 4 3 + 4 = 7 So… 7 – 4 = 3 4 x 3 =12 So … 12 ÷ 3 = 4 3 x 4 = 12 So … 12 ÷ 4 = 3

  20. Property 2:Commutativity Does it matter which way round the two operations are done? 4+3= 3+4= Does it matter in which order you add these numbers together? 15 + 7 + 5 + 3 = Addition is commutative Which of the other operations are commutative?

  21. Property 3: Associativity How would you do this, which pair would you start with? • 18+36+4= Does … (18+36)+4 = 18+(36+4) Is addition associative? Now try these, put the brackets in different places so that you start with different pairs. • 12 – 7 - 2 • 2 x 3 x 4 • 12 ÷ 6 ÷ 3 Which are associative?

  22. Property 4: Distributive 7x 13 = 7 x (10 + 3) = (7 x 10) +(7 x 3) 10 3 7 Is division?

  23. Summary 1Models, Links and Properties ● taking away from a set ● combining sets ● counting on or back (number line) ● counting on (number line) ● difference between INVERSES Commutative Neither Associative

  24. Summary 2Models, Links and Properties ● repeated addition ● repeated subtraction ● sharing ● lots of / groups of ● arrays ● groups of ● scaling INVERSES Commutative Neither Associative Distributive over addition

  25. EYFS 2013 and National Curriculum 2014 EYFS Early Learning Goal: • Use quantities of objects to add and subtract two single digit numbers • Count on and count back to find answers National Curriculum 2014: • Solve problems using concrete objects, pictorial representations and arrays (year 1/2) • Use inverse relationships to check addition and subtraction calculations (year 2)

  26. Cont…. • Show that addition of two numbers can be done in any order (commutative) and subtraction cannot (year 2) • Show that multiplication of two numbers can be done in any order (commutative) and division cannot (year 2) • Estimate the answer and use inverse operations to check answer (year 3) • Solve problems with scaling (year 3) • Use commutativity in mental calculations (year 4) • Solve problems using distributive law (year 4)

  27. Mental Strategies

  28. Rover has left his bone on the other side of the road. He can only get there by treading on boxes with an answer that is 7 (number bonds)

  29. Mental Strategy 1: Number Bonds • Not just number bonds for 10 • Extend to number bonds for numbers up to 20 • Make it visual for understanding Useful apparatus: Cuisenaire / Colour rods Numicom 8 6 + 2 https://www.ncetm.org.uk/resources/40533 3 + 4 7

  30. Mental strategy 2: Partitioning Use arrow cards to help children deconstruct numbers and combine multiples of hundred / ten / ones. (Later on introduce exchanging) 1 4 2 3 43 + 21 = (40 + 20) + (3 + 1) Links to associativity https://www.ncetm.org.uk/resources/40534

  31. Mental strategy 3: Bridging through 10 To use this strategy children first need to know number bonds to 10 and partitioning. Start visually using apparatus such as Nubicom / Colour Rods: 8 5 8 2 3 Children need to know number bond of 8 to make 10 5 is partitioned into 2 + 3 This is then extended to 2 digit numbers and the apparatus is replaced by empty number line jotting (covered later)

  32. Mental strategy 4: adding / subtracting 9 29 + 9

  33. Strategy 5: Complementary Addition Or subtraction by addition. 200 – 56 How could you model this? In this calculation you are looking at the size of the gap between the two numbers. 4 40 100 56 60 100 200

  34. Other Mental Strategies:KS1 • counting on • using known facts e.g. doubles • derive facts e.g. near doubles • counting on/back in ones and tens • adding or subtracting 9 by adding or subtracting 10 and adjusting by 1 • looking for number bonds to 10

  35. Other Mental Strategies: KS2 • partitioning numbers and dealing with the multiples of 10 first • adjusting numbers e.g. up or down to the nearest 10 • using known facts to derive new facts • looking for number bonds of 10 or 100, especially when adding together more than two numbers • subtraction using complimentary addition and compensation methods

  36. Try these….using mental strategies • 47 + 32 = • 39 + 18 = • 401 + 395 = • 57 - 29 = • 1000 - 989 = Discuss your strategies

  37. Skills needed before introducing Multiplication and Division Mental Strategies • Working out 3x4 by counting out three groups/sets of four • Counting in equal jumps along the number line – ‘five, ten, fifteen, twenty’ • Starting with tables for 1,2 and 10, knowing by heart facts such as ‘four tens’& progressing to facts in 5x table, then others • Recognising that multiplication can be done in any order – eg realising that 5x2 is the same as 2x5 – commutativity

  38. Learning Multiplication Tables • Children need to understand what multiplication tables are. 5 x 3 is displayed in stamps 2.They need to understand the commutative law

  39. Counting in 2s

  40. Counting in 4s

  41. Developing Multiplication and Division Mental strategies 1. Building on known facts: If you know 3x5=15… what else do you know?

  42. Developing strategies 2. Multiply and divide by multiples of 10 with whole and decimal numbers (link to place value) 3. Doubling and Halving

  43. Have a go • 509 x 3 • 5 x 23 x 20 • 112 ÷ 8 • 750 ÷ 25 Which strategies did you use?

  44. Issues: Mental Calculations • methods are all valuable if they are quick and accurate • emphasis on place value and usually work from left to right • May involve adjusting numbers • Need a distinction drawn between special cases and general strategies – a repertoire from which you select according to the particular numbers • Need to be explained in words and described using correct equations (partly to check understanding) • May be accompanied by structured jottings

  45. Structured Jottings • Reflect and support mental strategies • May need to be tidied up for an audience • Should lead to shortened forms • Are flexible

  46. Examples of children’s jottings Children’s recording in Reception Yr 1. My shepherd looks after 8 sheep but has lost 5 and he has 3 left..

  47. Key Stage 1 examples: Children’s recording in Year 2 1. Write the answer: 51- 27 = 24 3 + 20 + 1 Taken from Standards at Key Stage 1, QCA 2001 p.37 2. Write the number that is half of 38 30 + 8 15 + 4 As above, p 39

  48. Open number lines 25 + 38 33 2 23 5 38 40 63 25 30 63 Answer 63 246 – 78 using complementary addition and looking at the difference 20 2 146 78 80 100 246 Answer 146 + 20 + 2 = 168

  49. Ofsted 2011 Stresses the importance of children demonstrating a fluency in calculating, solving problems and reasoning about number. Key findings: Practical, hands-on experiences are crucial in EYFS and KS1 couple with opportunities to develop mathematical language. Understanding place value, fluency in mental methods and good recall of number facts. Subtraction should be taught with its inverse addition and division taught alongside its inverse, multiplication.

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