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why is this defeating dd? Simpe arithmatic`

(20 Posts)
ontheedgeofwhatever Tue 20-Nov-12 12:36:43

dd''s homework included the question how much would 2 apples cost if one is 14p? She said 18p so I broke it down.

First I asked her what is 10p + 4p and she said 14p.
then I asked her what is 14p + 4p she said 18p
then I asked her 18p plus 10p and she said 28p
then i said what is 10p + 10p + 4p + 4p and again she said 28p

So what is 14p + 14p. 18p confused

I tried it from a number of different angles. I gave her 28 felt tips and told hertocount out 14 and then another 14 and tell me how many there were all together and she said 28 yet when I said so what is 14+14 she said... 18.

Why what am i doing wrong? She does this with any simple sum that adds up to more than 20.

(she's 7 and in year 2)

legalalien Tue 20-Nov-12 12:48:26

Well, not every sum if she got 18p plus 10p right?

No idea I'm afraid.

mummytime Tue 20-Nov-12 12:49:25

Can you do it with coins? Get her to play shop keeper. Buy one apple 14p, then remember and buy another at 14p, give it to her in change, now get her to see how much she has got in total.
I would also talk to the teacher just in case it is a case of "I believe the teacher said X, there fore it must be true" even though she has misheard/understood.

learnandsay Tue 20-Nov-12 12:51:02

Let her do it herself with pens, raisins, and blocks of lego. And then let her do it on a number line, with a number square and on a Melissa & Doug abacus. Then let her "make" the sum and other sums with wooden numbers and symbols, if you have them, or cut them out of paper. And finally let her write the sum out on paper (with several other similar sums.)

(The problem is jumping from the concrete to the abstract in one go. Fourteen pens are concrete, but the questions what is fourteen plus fourteen is an abstract one.)

Brycie Tue 20-Nov-12 12:52:45

Hasn't she done take away at school, why is it all about adding.

YDdraigGoch Tue 20-Nov-12 12:53:32

Can you show her the old fashioned way, by writing one number under the other, and labeling each column Tens and Units? Then you add up the tens, and you add up the units.

T U
1 4
1 4
-

===

Can she get it right with other numbers (13+15) for example?

Brycie Tue 20-Nov-12 12:53:47

Why don't you do take away with her with two apples and fourteen pennies. Making it lego blocks is even more abstract. Get some apples, get some pennies and do a take away thing.

Brycie Tue 20-Nov-12 12:54:39

Or do columns. Columns are good, goch is right.

HeathRobinson Tue 20-Nov-12 12:55:41

You could try some addition games in the maths zone of Woodlands Junior School?

crazygracieuk Tue 20-Nov-12 13:22:49

My son is in Y2 and would have worked out that he's being asked 14+14.

He'd probably use a 100 square and start at 14, move to 24 (+10) then +4 or use a number line with the same jumps +10 then +1 +1 +1 +1.

maizieD Tue 20-Nov-12 16:53:34

I wonder if, when you 'asked' her the various calculations, she got the ones correct that involved adding units to a double figure just by counting on, whereas adding the tho 'double' figures together mentally was just a bit too difficult? Was she doing this on paper or 'in her head'?

I agree that column addition makes the operation very explicit. The visual aspect of it may help, too. I'm too old to know about the methods suggested by crazygraceuk sad

strictlovingmum Tue 20-Nov-12 17:15:55

Agree with goch,
but would add units first and then tens, in the case of 14+14 it doesn't really matter which way first but in any future additions total of units if exceeding ten will affect total of tens, so

T U
1 4 (1)
1 8

-
3 2

There will be carrying so it is good to show them the right way around, units first then tens.

mrsbaffled Tue 20-Nov-12 18:41:34

It's all about number lines at this age x

LauraSmurf Tue 20-Nov-12 18:41:52

Try to partition it for her:

14. +. 14
/. \. /. \
10 4. 10 4

Then add the tens then the fours.
This is actually a mental method, it's how most of us do mental addition, well one of the methods anyway!

Try that???

ontheedgeofwhatever Tue 20-Nov-12 18:58:11

Thank you I will try some of these.

Oddly though there was a note from her teacher in her home book tonight saying "thank you for working with ontheedgejunior on adding number coming to over 20 she suddenly seems to have understood it"

Children are odd -confused

choccyp1g Tue 20-Nov-12 19:28:04

I'd try it with real money. The concept of tens and units is clearer if you use 10p and 1p pieces.

CameronSmith Tue 20-Nov-12 19:46:33

Another vote for number lines at this age.

legalalien Tue 20-Nov-12 19:56:43

I hated number lines and if I have my way ds will go nowhere near them (he's got as far as y3 without them, am I safe?). Columns, I tell you, all about understanding how the numbers are put together. I explained different bases to ds at an early age (they were explained to me at an early age) and it helped a lot.

MasterOfBuggerAll Tue 20-Nov-12 20:15:38

As a child and as an adult, mental arithmetic is completly beyond me. My mind simply does not work that way. I can understand the theory and application, however I need a calculator.

It was only as I became an adult I realised I am not mathematically minded.

Now my DM would rival Carol Voderman. She used to get angry at me for not being able to do simple maths.

What I am trying to get at, is yes try to help her, but don't make her feel inadequate for not being able to.

strictlovingmum Tue 20-Nov-12 20:21:47

I am not pro or against number line(DH is against), but now in Y2 dd is not allowed to use one in the classroom anymore, and I am pleased with that.
I tend to favour columns over number line, we did it with DS 18 worked for him, started with DD year ago and it works for her, she will add and subtract any two numbers with carrying/borrowing accurately and reliably, understands the money concept, in general she excels in maths.
We do a lot of maths at home and we do it our way, lot of it is verbal without any recording on paper, practice x,+,- on the way to school 5 to 10 minutes every morning, never used any app. or computer program with either one of them, so far served them well.
Agree with legalalien starting early on also worked for me and my dc's, as for different method being used at home from the one used at school risking getting children all confused and muddled up, IME we had no experience of that, rather the opposite.

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