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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

yes i understed all of that? so what is next?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

So:

2 . 6 +

3 . 5

--------

6 . 1

--------

1

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

now what do you what me to do?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

By the way the answer 6.1 does have a decimal point in it. (Bob left this out of his graphic)

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

OK here is what I suggest. How about you try an example like 5.7 + 3.6 and see how you get on with that.

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

so what should we do then?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

OK here is the problem:

5 . 7

3 . 6

--------

--------

What is the first step in solving this addition ?

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

so 5 . 7 + is this right then?

3 . 6

------

9. 3

-------

1

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Yes well done. Correct.

Right how about 3.57 + 6.69 ?

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

is it like 3 . 5 7

6 . 6 9 +

--------

10 . 2 6

---------

1 1

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

3 . 5 7 +

6 . 6 9

-----------

----------- ???

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Sorry about that I realise that you have posted at about the same time that I posted that.

Yes well done you are correct again.

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

If you had three things to add together like 1.78 + 2.89 + 3.67 what would you do ?

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

i would first put them in a coloum?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Yes so you could put them all in one addition if you wanted. Like this

1 . 7 8

2 . 8 9

3 . 6 7

---------

---------

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

so now what?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

I have noticed that you are quite good at these sums. Are you okay with 10.69 - 8.78 ?

Do you want to have a go at that one ?

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

i am not sure how to do this?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Right first let's write it out in full:

1 0 . 6 9

8 . 7 8

-----------

-----------

Now the first bit is easy. 9 - 8 = 1.

So in the answer the number one can be written straight away.

1 0 . 6 9

8 . 7 8

-----------

1

-----------

Now in the next stage 6 - 7 = -1 this is a problem because we need a number between

0 and 9. I would then look to the left of the top number. In the next column there is a "0".

This is no good: We cannot decompose a zero.

So: Look at the far left at the top. We have a one so we can take 1 away from this to get

zero. Then we can drop off a "9" in the next column to the right. Then drop off a "10" to

the right of this (notice that we are just redistributing the number here - 10.0 = 9.0 + 1.0).

9 . 16 9

8 . 7 8

------------

1

------------

Right I will give you a minute to look at that and ask any questions about that bit....

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

ok i have looked at that now what?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Right now the subtraction can be done quite easily:

9 . [16] 9 -

8 . 7 8

-------------

1 . 9 1

-------------

By the way I need to mention a few points before I teach you any bad habits.

There are limits to what I can display at this speed, online via a maths forum.

I have had to adapt the way I would usually write subtractions considerably.

If you have to attend an exam on subtraction (and other topics) then please follow

the conventions in your course about how to present your answer.

When I was taught how to do subtraction I would cross out the "1" and put a zero

The "0" to the right would be crossed out and replaced by a 9.

The 16 would be written with the "1" superscripted slightly to indicate that it had been

put in afterwards etc. Method marks are often more important than getting the correct answer.

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

ok what should i do now then?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

OK. How about you try 20.37 - 18.66 ???

Try to indicate how you worked out the answer as well as you can.

There are limits to what you can do in plain text.

I will probably be able to see if you have used a sensible method.

Good luck.

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**mandy jane****Member**- Registered: 2010-09-23
- Posts: 988

first put in colcum 2 0 . 3 7

1 8 . 6 6-

----------

then - 7-6=1 then 3-6 don'tgo so take 1 from the 2 which makes that 1 put 1 next to the 0 now is 10 so take 1 from the 10 makes that 9 and put 1 next to the 3 wichis now 13 so 13-6 =7 so put 7 in senden colcum .9-8=1 so put in threed colcum and 1-1 = 0 put in forth colcum so it looks like this?

2 0 . 3 7

1 8. 6 6 -

----------

0 1 . 7 1

----------

is this right?

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**SteveB****Member**- Registered: 2013-03-07
- Posts: 547

Very good. Correct answer.

Can you see how to do 5 .69 - 3.78 ?

If you can do it then go ahead. I wll explain it if you need help.

Another one you might like to try is: 1.3 - 0.716 ?

Notice here that the decimals are not the same length so care is needed with positioning

and place value.

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