# Equal addition making a comeback?

Discussion in 'Primary' started by tandemtinker, Jan 31, 2019.

1. ### tandemtinkerNew commenter

I've just looked at my grand daughter's math's homework ( Y5 ] and was surprised to see a return to my own childhood's equal addition for mechanical subtraction....on questioning her, I found that she and her class prefer this method and the teacher lets them choose! Am I behind the times or is this "ancient" method on the way back!!

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3. ### MilgodEstablished commenter

I've never used it and I'm not entirely sure why anyone would. Seems longer than normal 'column' subtraction which takes seconds to do.

4. ### Lara mfl 05Star commenter

Oh I thought I'd replied to this?

Am I missing something, but when we did it 'equal addition' was the column method? You just 'borrowed' and 'added' to the next column.

Vince_Ulam likes this.
5. ### caterpillartobutterflyStar commenter

It's VERY long winded.

It depends how long ago you learned, and also who you learned from. The rest of my class did decomposition, but I "borrowed and paid back" because my mum had shown me that. The teacher was quite happy for me to carry on, but I got another bright kid to teach me decomposition because when other kids asked me for help I needed to know what they were doing.
I once borrowed and paid back in front of a class without thinking - they were fascinated and wanted me to explain what I was doing.
Where equal addition does better is when there is a 0 in the middle of the larger number, because decomposing across two columns is fiddly.

7. ### MilgodEstablished commenter

Tbh, I still don't see how the equal addition method would be quicker even with a something like 23006 - 2434. Two zeros to deal with there but not exactly time consuming.

I'm probably missing something though as I never used it.

8. ### Lara mfl 05Star commenter

not sure if this will format but surely this doesn't take long?
2 31010 6

- 2 54 3 4

2 1 5 7 2

9. ### MilgodEstablished commenter

Not sure what you're trying to show tbh.

10. ### caterpillartobutterflyStar commenter

I don't think that is equal addition though.
Youtube says you add the same thing to both numbers to make the subtraction easier.
But I'd say you have to pretty good at mental addition to make it work and it takes ages!

23006-2434
=23006+6 - 2434+6 = 23012 - 2440
=23012+60 - 2450+60 = 23072 - 2500
=23072+500 - 2500+500 = 23572 - 3000
=20572

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11. ### Lara mfl 05Star commenter

Grr. Took me ages to write this out . . the then tes lost my post. Should have saved it of course.
It is equal addition, because each time you borrow you do the same to the column you've borrowed from .
Actually if you think in terms of columns all the time it is easier'.

So starting with the units column
6
- 4
= 2
quite simple as no borrowing involved.

Then look at the tens column

10 6 can't take 3 from 0, so 'borrow' / add 100 from h..column
- 54 3 4 & add 100 to the 400 making it 500/ 'doing the same'
= 7 2 ( 100 - 30)

hundreds column
10 0 6 can't take 4 from 0, so add 1000 from th. column
32 54 3 4 & add 1000 to 2000, making it 3000- to add the same i e equal
= 5 7 2 because now is 10 - 5

thousands column
3 0 0 6 (don't need to add or equalise)
- 324 3 4 (2000 became 3000 from previous equalisation)
= 0 5 7 2 because now became 3 - 3

and finally 10 th,
2 3 0 0 6
- 2 4 3 4 again simple as nothing to take away.
2 0 5 7 2

So it's not as complicated and I'm not maths trained, so hope that makes it somewhat clearer.
Arrgh! And now the formatting's gone. took me half an hour and now the columns won't go where I put them. Perhaps try in QUOTE mode as it seems to show up correctly In preview?

Last edited: Feb 9, 2019
guinnesspuss likes this.
12. ### caterpillartobutterflyStar commenter

Ahhhh welll...
It does look better in quote mode.
I agree it isn't complicated, but it is long winded and has more steps than simple decomposition.

I think we all prefer the method we learnt at school and for most of us it works brilliantly.
I spent hours and hours doing 'tens and units sums' (both addition and subtraction...ooops) from what was then middle infant all the way to top junior(Year 1 to year 6). I was brilliant at them and loved them. Maybe if we'd had to learn 47 different methods and choose our own, I'd not have liked it so much. Not sure.

13. ### guinnesspussStar commenter

Well done Lara.
I learned the 'equal addition' way, but my mum was taught decomposition in the 1930's. Those people who 'know best' (aka advisors et al.) decided decomp was the way to go. I find eq add by far the easiest, but it isn't mathematically sound apparently - though it does the job.

Lara mfl 05 likes this.
14. ### guinnesspussStar commenter

Some of us have been made to feel incompetent over the years because we weren't doing the correct method.

Lara mfl 05 likes this.
15. ### MilgodEstablished commenter

Because it's slower and makes less sense is all.

16. ### MilgodEstablished commenter

That's also not the version of equal addition that I've seen online. Plus, still slower than decomposition and makes less mathematical sense.

17. ### guinnesspussStar commenter

You like best what you learn, I think. I can do either just as fast.
Because Mum showed me her way, I could understand what the advisors were saying when it became the fashion/dictum to use decomp. The same has happened with division.

Lara mfl 05 likes this.
18. ### MilgodEstablished commenter

Right, but decomp makes more mathematical sense in the sense of subtraction.

Lara mfl 05 likes this.