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L.O.1 To be able to use known facts and place value to multiply and divide mentally.

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Presentation on theme: "L.O.1 To be able to use known facts and place value to multiply and divide mentally."— Presentation transcript:

1 L.O.1 To be able to use known facts and place value to multiply and divide mentally.

2 Answer these on your whiteboards: What are 10 lots of 5? What is the product of 20 and 5? What is 30 multiplied by 5? What are 10 lots of 6? What is the product of 20 and 6? What is 30 multiplied by 6?

3 As 20 is double 10 so 20 x 6 = double 10 x 6 20 x 6 = 2 x (10 x 6) = 120

4 As 30 is treble 10 so 30 x 6 = treble 10 x 6 30 x 6 = 3 x (10 x 6) = 180

5 As 40 is quadruple 10 so 40 x 6 = quadruple 10 x 6 40 x 6 = 4 x (10 x 6) = 240

6 As 50 is quintuple 10 so 50 x 6 = quintuple 10 x 6 50 x 6 = 5 x (10 x 6) = 300

7 Q. How many 6s are there in 120? How do you know? 120 = 12 x 10 so 120 ÷ 6 = (12 ÷ 6) x 10 = 2 x 10 = 20

8 What are the answers to these? 180 ÷ ÷ ÷ ÷ ÷ ÷ ÷ 6

9 LOOK… 180 ÷ 6 = (18÷6) x 10 = 3 x 10 = ÷ 6 = (24÷6) x 10 = 4 x 10 = ÷ 6 = (30÷6) x 10 = 5 x 10 = ÷ 6 = (36÷6) x 10 = 6 x 10 = ÷ 6 = (42÷6) x 10 = 7 x 10 = ÷ 6 = (48÷6) x 10 = 8 x 10 = ÷ 6 = (54÷6) x 10 = 9 x 10 = 90

10 What are the answers to these? ÷ ÷ ÷ ÷ ÷ ÷ ÷ ÷ 8

11 LOOK… ÷ 4 = (240÷4) = 6 x 10 = ÷ 5 = (250÷5) = 5 x 10 = ÷ 2 = (180÷2) = 9 x 10 = ÷ 4 = (200÷4) = 5 x 10 = ÷ 7 = (280÷7) = 4 x 10 = ÷ 9 = (540÷9) = 6 x 10 = ÷ 2 = (160÷2) = 8 x 10 = ÷ 8 = (320÷8) = 4 x 10 = 40

12 L.O.2 To be able to approximate; extend written methods to short division of HTU by U; estimate by approximating then check results.

13 We are going to use a shorter written method for division. 183 ÷ 5 Q. Approximately how many fives are there in 183?

14 183 ÷ 5 We know that 30 x 5 = 150 We know that 40 x 5 = 200 so as 183 comes between 150 and 200 our answer lies somewhere between 30 and 40

15 Using chunking… Watch carefully! We can start by using the LOWER of our two estimates… ( 30 x 5) ( 6 x 5) 30 3 Answer = 36 r.3 Q. Is 36 r.3 likely to be correct? How do you know?

16 Try this on your own. When you have an answer compare it to your partners. 147 ÷ 6

17 There is a similar method called short division. Our sum is 183 ÷ 5 CHUNKING SHORT DIVISION 36r (30 x 5) (30 x 5) (6 x 5) - 30 (6 x 5) 3 3 Answer = 36r.3 How are these sums similar? How are they different?

18 Try these: Use the SHORT DIVISION method. Approximate the answers first. Use the LOWER multiple of the divisor as the first subtraction ÷ ÷ ÷ ÷ ÷ ÷ 6

19 Answers?? ÷ ÷ ÷ ÷ ÷ ÷ 6 Q. Do the answers seem to be correct compared to the approximations? Check your own answers. Where have you gone wrong?

20 By the end of the lesson the children should be able to : Use short division to divide HTU by U; Approximate results first and use the approximation to check whether results are reasonable


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