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PostPosted: Tue Jun 22, 2010 7:28 pm 
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Why do many teachers and textbook teach children, in the early stages of addition and subtraction, to deal with the tens before the units? Just seems wrong to me, and more likely to lead to problems later on. Is there a reason that I have missed?


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PostPosted: Tue Jun 22, 2010 7:42 pm 
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Off the top of my head :) is it to do with number lines and number bonds? I tried to work an example and failed. :roll:

I do understand and sympathise with the question as it seems to build such a big, almost unnecessary, jump later on to column maths.

Having said that..............teachers do know best. :wink:


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PostPosted: Tue Jun 22, 2010 8:02 pm 
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I think it all comes down to partitioning...

12 = 10 +2

22= 20 +2

am still trying to workout why you have to work from higher to lower, by the time I have I am sure there will have been another strategy and I will have to start all over again....
:roll:


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PostPosted: Tue Jun 22, 2010 11:09 pm 
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This baffled me too. It seems entirely counter intuitive and confused both DD and me

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PostPosted: Wed Jun 23, 2010 8:11 am 
I am afraid that I actually quite like this method and taught my youngest it and she is fairly good at arithmetic. I have also noticed my 11 plus pupils who do tens first are much quicker than the ones who can't add across the way and have to write down any sum as a column addition.

Thus if you had:

26 + 15 + 37 + 44

they would go 26...36...41...71...78...118....122.

Doing it the other way, you risk them forgetting what they are carrying or reversing it.

Obviously if you are formally writing it in columns, you would do units, then tens, but the above technique is meant to be applied to mental arithmetic where you are only going to write the answer.


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PostPosted: Wed Jun 23, 2010 8:27 am 
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The above method as demonstrated by FM is the way I've always done it myself for the past ahem years (over 40 :oops: ) - didn't realise it was something new!

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PostPosted: Wed Jun 23, 2010 8:34 am 
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Snowdrops wrote:
The above method as demonstrated by FM is the way I've always done it myself for the past ahem years (over 40 :oops: ) - didn't realise it was something new!


Ditto! :)


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PostPosted: Wed Jun 23, 2010 8:56 am 
What's that expression: there is nothing new under the sun.

And certainly this method isn't because I have been using it for 50 years.

But maths methods come and go like fashions,and should be treated as such. If the fashion doesn't suit you, then try wearing something else. For instance, after many years of trying to teach my innumerate (is that a word?) son decomposition subtraction, I reverted to doing borrow one, pay back one, and he had it pat in an hour.


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PostPosted: Wed Jun 23, 2010 3:15 pm 
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actually fm, when I see it written down I realise that that is the way I add up mentally.

The way maths is taught these days is far more about having a feel for number and understanding than just doing a standard algorithm and not having any idea whether or not the answer made sense.


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PostPosted: Wed Jun 23, 2010 8:38 pm 
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Yes - it's a mental method. I start with highest value digits when working mentally. If I work on paper start with lowest value digits.
Children are taught to use mental methods with informal jottings, numberlines etc, then move on to more formal methods as their understanding of the number system develops.


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