l.o.1 to be able to use known facts and place value to multiply and divide mentally

L.O.1To be able to use known facts and place

value to multiply and divide mentally.

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?

As 20 is double 10

so 20 x 6 = double 10 x 6

20 x 6 = 2 x (10 x 6)

= 120

As 30 is treble 10

so 30 x 6 = treble 10 x 6

30 x 6 = 3 x (10 x 6)

= 180

As 40 is quadruple 10

so 40 x 6 = quadruple 10 x 6

40 x 6 = 4 x (10 x 6)

= 240

As 50 is quintuple 10

so 50 x 6 = quintuple 10 x 6

50 x 6 = 5 x (10 x 6)

= 300

Q. How many 6’s are there in 120?How do you know?

120 = 12 x 10

so 120 ÷ 6 = (12 ÷ 6) x 10

= 2 x 10

= 20

What are the answers to these?

180 ÷ 6

240 ÷ 6

300 ÷ 6

360 ÷ 6

420 ÷ 6

480 ÷ 6

540 ÷ 6

LOOK…

180 ÷ 6 = (18÷6) x 10 = 3 x 10 = 30

240 ÷ 6 = (24÷6) x 10 = 4 x 10 = 40

300 ÷ 6 = (30÷6) x 10 = 5 x 10 = 50

360 ÷ 6 = (36÷6) x 10 = 6 x 10 = 60

420 ÷ 6 = (42÷6) x 10 = 7 x 10 = 70

480 ÷ 6 = (48÷6) x 10 = 8 x 10 = 80

540 ÷ 6 = (54÷6) x 10 = 9 x 10 = 90

What are the answers to these?

1. 240 ÷ 4

2. 250 ÷ 5

3. 180 ÷ 2

4. 200 ÷ 4

5. 280 ÷ 7

6. 540 ÷ 9

7. 160 ÷ 2

8. 320 ÷ 8

LOOK…

1. 240 ÷ 4 = (240÷4) = 6 x 10 = 60

2. 250 ÷ 5 = (250÷5) = 5 x 10 = 50

3. 180 ÷ 2 = (180÷2) = 9 x 10 = 90

4. 200 ÷ 4 = (200÷4) = 5 x 10 = 50

5. 280 ÷ 7 = (280÷7) = 4 x 10 = 40

6. 540 ÷ 9 = (540÷9) = 6 x 10 = 60

7. 160 ÷ 2 = (160÷2) = 8 x 10 = 80

8. 320 ÷ 8 = (320÷8) = 4 x 10 = 40

L.O.2

To be able to approximate;

extend written methods to short division of HTU by U;

estimate by approximating

then check results.

We are going to use a shorter written method for division.

183 ÷ 5

Q. Approximately how many fives are there in 183?

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

Using chunking… Watch carefully!

We can start by using the LOWER of our two estimates…

183

- ( 30 x 5)

150

33

- ( 6 x 5)

30

3

Answer = 36 r.3

Q. Is 36 r.3 likely to be correct? How do you know?

Try this on your own. When you have an answer compare it to your partner’s.

147 ÷ 6

There is a similar method called short division.

Our sum is 183 ÷ 5 CHUNKING SHORT DIVISION

36r.3 183 5 183 -150 (30 x 5) - 150 (30 x 5)

33 33 - 30 (6 x 5) - 30 (6 x 5) 3 3

Answer = 36r.3

How are these sums similar? How are they different?

Try these:Use the SHORT DIVISION method.

Approximate the answers first.

Use the LOWER multiple of the divisor as the first subtraction.

1. 154 ÷ 5

2. 176 ÷ 5

3. 188 ÷ 5

4. 237 ÷ 4

5. 169 ÷ 6

6. 222 ÷ 6

Answers??

1. 154 ÷ 5

2. 176 ÷ 5

3. 188 ÷ 5

4. 237 ÷ 4

5. 169 ÷ 6

6. 222 ÷ 6

Q. Do the answers seem to be correct compared to the approximations?

Check your own answers. Where have you gone wrong?

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