Cut and Paste

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Cut and Paste I am learning to solve multiplication problems using doubling and halving, thirding and trebling, and other proportional adjustments. X 2 2 3 X 3

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Cut and Paste. I am learning to solve multiplication problems using doubling and halving, thirding and trebling, and other proportional adjustments. 2. X 2. 3. X 3. To start with lets use ‘doubling and halving’ to help us change a question and make it easier to answer. - PowerPoint PPT Presentation

Transcript of Cut and Paste

Cut and Paste

I am learning to solve multiplication problems using doubling and halving, thirding and trebling, and other proportional adjustments.

X 2 2

3 X 3

To start with lets use ‘doubling and halving’ to help us change a question and make it easier to answer.

Below are 4 groups of 3 or 4 X 3 = 12

Now let’s halve the number of groups there are.

4 X 3 = 12

2 X …. = 12

Do this by dividing by 2

Then double the amount you put in each group.

Do this by multiplying by 26

So…4 X 3 = 12

and

2 X 6 = 12

÷2 x2

Now let’s try a thirding and trebling example.

Below are 3 groups of 27 or 3 X 27 = ?

Now let’s triple the number of groups there are.

3 X 27 = ….

9 X …. = ….

Do this by multiplying by 3

Then third the amount you put in each group.

Do this by dividing by 3

9

9 X 9 = 81so 3 X 27 =81

81

We can also adjust our problems more than once if it helps.

2 X 36 = ?

4 X 18 = ?

8 X 9 = 72

X2

X2

÷2

÷2

Doubling and halving once didn’t help so we can do it again.

We could also have divided by 4 and multiplied by 4. This would have saved us the middle step and we would still have got the same answer.

÷4X4

The questions on the left have a buddy question to the right where, doubling and halving or trebling and thirding has been used. Which questions do you think go together?

1) 5 X 14 = ?

2) 14 X 50 = ?

3) 6 X 18 = ?

4) 3 X 24 = ?

Click again when you have worked out which questions go together.

10 X 7 = 70

7 X 100 = 700

12 X 9 = 108

9 X 8 = 72

Use doubling and halving to help you work out the answers to these questions.

1) 18 X 5 = ?

2) 21 X 3 = ?

3) 6 X 25 = ?

4) 33 x 3 = ?

5) 4 X 50 = ?

Click again when you have worked out all your answers.

9 X 10 = 90

7 X 9 = 63

3 X 50 = 150

11 X 9 = 99

2 X 100 = 200

Need some more practise? Try Pg31 & 32 of Teacher Tools Multiplication and Division Book Numeracy resources