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Adding two digit numbers

(11 Posts)
schmee Sun 06-Jan-13 17:43:38

My son is in year one and can add single digit numbers well. He struggles with adding sets of two digit numbers though (without carrying at this stage). Can anyone tell me how this is taught in schools nowadays?

Thank you very much.

SpottyBagOfTumble Sun 06-Jan-13 17:46:04

They split the numbers. So 23 + 45 would be 3 + 5 then 20 + 40. I think it is called partitioning.

schmee Sun 06-Jan-13 17:52:39

Thank you - I will google partitioning and see what I can come up with!

KingscoteStaff Sun 06-Jan-13 18:59:55

Check that he really understands how 2 digit numbers are created - that 34 means 3 lots of ten and 4 units.
Do lots of practice partitioning them like this.

Then practice adding multiples of 10 together: 3 + 4 = 7,
3 tens + 4 tens = 7 tens
30 + 40 = 70

Once he can partition and add multiples of 10 confidently, then he's ready to add 2 2-digit numbers:

25 + 42
20 + 5 + 40 + 2
20 + 40 = 60
5 + 2 = 7
60 + 7 = 67

Now check that he can add a 'teens' number to a multiple of 10 in his head
- eg for 50 + 14 he should be thinking "well 50 + 10 is 60, and another 4 is 64"

Once he can do this confidently, then try some 2 digit + 2 digit where the units add up to more than 10 :

37 + 45
30 + 7 + 40 + 5
30 + 40 = 70
7 + 5 = 12
70 + 12 = 82 ("70 + 10 is 80 and another 2 is 82")

As a Year 6 teacher, I can tell you that getting a good understanding of what he is doing is vital for all his future maths. He needs to gain confidence 'mucking about with numbers'.

Keep it going - you are doing exactly the right thing!

Houseworkprocrastinator Sun 06-Jan-13 20:10:35

I agree it is really important to have a proper understanding of what a number is. I think once they grasp this everything else will come relativity easily. It may help using props like lego show the tens and units. I used to teach an adult maths class and it was amazing how many people went all the way through school learning maths by rote but not actually understanding what they were doing.

schmee Sun 06-Jan-13 20:22:31

Thank you all of you. Kingscotestaff - from what I can tell he doesn't really understand about of the tens and the ones making up the double digit. I was thinking of using smarties and little pots (to hold the tens) to try to explain this to him. Lego is a great idea housework as he loves that. We have been practising adding multiples of ten together (50 plus 30) so it's good to know we're on the right track with that.

My search on partitioning brought up arrow cards which seems like a great way of explaining it too. I'll try to find out if they are using them at his school.

He's quite bright so I think he has got this far just by common sense/seeing it in his head, but now it's getting slightly more difficult I'd really like to help him understand things better.

RiversideMum Mon 07-Jan-13 20:01:23

Like others have said, it's really fundamental that children understand that eg 14 is 10+4 or 56 is 50+6. I've taught HTU using pasta with older children who struggled with maths - which is a bit like your smarties idea. We started with a big pile of pasta and then organised it into little freezer bags each with 10 bits of pasta in. Then then 10 small bags went into a big bag to make 100. Dienes (sp) which a lot of schools use, work on the same principle.

KingscoteStaff Mon 07-Jan-13 20:26:00

Also useful are pencils - get your son to put them into bundles of ten with a rubber band. Count in 10s as you touch the bundles.

Then 24 is very clear - 2 bundles of 10 and 4 single pencils.

It also makes 24 + 32 very clear - add the bundles of 10 to make 5 tens, then add all the single pencils to make 6 - 56 altogether.

If you add 24 and 38, it becomes very clear that you have 5 tens and 12 units - get another rubber band and turn the 12 into 1 ten and 2 units.

I will be doing this tomorrow with one of my Year 6 children!!!!

EllenJaneisstillnotmyname Mon 07-Jan-13 20:47:58

In year 1 they may be using a number line to add a single/double digit number to a double digit number, also. So 23 + 5, start at 23 on the number line and count on 5 to 28. Or 23 + 15, count on in a jump of 10 to 33, then on another 5 to 38. Again, he'd have to understand how a double digit number works, in tens and units.

lljkk Mon 07-Jan-13 20:54:38

Ours would be all number lines, so 14 + 38 would be 14 + 30 = 44. then 44 + 8 = 52.

schmee Wed 09-Jan-13 11:57:47

Thank you. I will ask if they are using number lines. I think they were using them for single digit addition but didn't get the hang of them that well. This is all really helpful - thanks so much.

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