# Talk

## I need some maths help for my 7 year old please!!

(20 Posts)
Lunar1 Thu 07-Apr-16 11:18:43

Ds1 had been give long addition and subtraction sheets to do over the holidays. He has been doing really well without help but he's stuck, and so am I.

On subtraction a he's been doing well with borrowing from the next column, but the next question is,

300
-173

How should he be working this one out? Thank you in advance for any help.

Treetopchallenger Thu 07-Apr-16 11:21:22

Borrow from the three so you have a 10 in the top middle, then borrow from the 10. So you would have 2 9 then 10.

Lunar1 Thu 07-Apr-16 11:29:13

So would the second 0 be a 9, and a 10 in the units? Sorry, showing how bad I am at this here!!

yomellamoHelly Thu 07-Apr-16 11:29:15

You could also think of it in terms of number lines - so bridge to 180, then 200, then 300 and add the total of those bridges together - if he's having trouble getting the concept of carrying over twice.

Lunar1 Thu 07-Apr-16 11:30:12

He will get it once I explain it to him, it's me that will struggle

OneMagnumisneverenough Thu 07-Apr-16 11:32:28

method above is how I would do it, but schools do stuff funny nowadays

I found this book really useful - very well laid out too:

Lweji Thu 07-Apr-16 11:34:58

I work it out by considering the 0 on the top right as 10, subtract the 3 from it, so 7.
Then I add the 1 from the 10 to the 7 at the bottom, giving 8.
Then consider the middle 0 as 10 as well, and subtract the 8 from that 10, giving 2.
Then I add the 1 from that 10 to the 1 at the bottom and subtract the resulting 2 from the 3, giving 1.

So, 127.

Lunar1 Thu 07-Apr-16 11:38:38

Dh tried to explain the adding a number at the bottom method and that got me really confused. I've just had a go at them all with the method of changing the 3 to a 2 then 9, 10 which I seem to have managed. I may come unstuck in a min though it's got numbers in the thousands coming up.

Lweji Thu 07-Apr-16 11:42:00

You can also take from the left of each top number. It's just more confusing when you have a 0 there, but you just need to consider it a 10 and reduce to 9. You do have to then remember to take a 1 from its left too, as treetop said.

Thu 07-Apr-16 12:13:41

Forgive the sideways picture.
Taking it step by step, you have 3 hundreds. That's the same as 2 hundreds and 10 tens. 2 hundreds and 10 tens is the same as 2 hundreds, 9 tens and 10 units.

10 - 3 = 7 (units)
9 - 7 = 2 (tens)
2 - 1 = 1 (hundred)

300 - 173 = 127

Michaelahpurple Thu 07-Apr-16 15:35:07

I highly recommend rob eastaway's maths for mums and dads (no help with this homework but for the future!)

Not as coyly written as the title sounds and it goes through all the methods children are now taught

irvine101 Thu 07-Apr-16 15:47:44

My ds's school has calculation booklet for parents. It's also on web page.
Maybe ask the teacher if your dc's school have something like that? It really helps to know which method the school is using.

Thu 07-Apr-16 15:55:10

I'm a year 4 TA this is how we do it.

Thu 07-Apr-16 16:00:56

How embarrassing, I meant this of course! There's also the longer method.

ketchupontoast Fri 08-Apr-16 21:48:37

I have always exchanged from the next column but learnt a new way on a training course this year and trialled it with my class and they found it much easier than all the crossing outs and exchanging over multiple place values.
When there is a number with all other values as 0 - just subtract 1 from each value. The difference will remain the same but then you end up with all 9s on the top so no exchanging. 300 - 173 would change to 299 - 172. The amount of numbers between the values are the same so you will get the same answer without any exchanging. Not sure if your child will be allowed to do that in class but my class love it as a method.

irvine101 Fri 08-Apr-16 22:03:26

ketchupontoast, first I thought what a brilliant method. But then I thought if it create even more confusion and mistakes, especially for less able children? Like, take away 1 from 300 but forgets to take away 1 from 173, etc.

ketchupontoast Fri 08-Apr-16 22:25:42

I find that if they understand the concept then they can usually come up with the procedure themselves. If they only understand the procedure and not the concept then it brings about issues...same with all maths procedures. Hence why children make mistakes in their procedures as they are sometimes taught how to get to an answer by following steps to success but they don't actually get the concept so don't appreciate if they make a mistake. I taught the concept with small numbers first so like 8-2 changing to 7-1 using a visual and so the children saw how the difference stayed the same but we were just using the numbers one less than. They then explored if this happened with 2 digit numbers etc. I gave them a problem similar to the one asked and the children used their understanding of the concept to tell me what they would do...I didn't have to teach it to them as they applied their knowledge to the algorithm from using the visual models.

irvine101 Fri 08-Apr-16 22:36:47

I see. If you teach that way, they may have a big advantage doing more complex works in the future. Ok, I think it's brilliant.

ketchupontoast Fri 08-Apr-16 22:47:47

I think it is too! So much easier than all that crossing out!

RafaIsTheKingOfClay Sat 09-Apr-16 09:05:00

It is a good method. Although I think I'd like children to know both.

I definitely agree about understanding how and why the procedure works though. I think that's a step that can often be missed in teaching formal column methods when you need to borrow.

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