# Talk

## 3 digit column subtraction

(10 Posts)
MadHousewife2 Thu 23-Jun-16 13:28:20

Hi there - can anyone help me explain to DD how to set out and do the following sum please?

906
- 387
__
__

Many thanks

MadHousewife2 Thu 23-Jun-16 13:31:22

Sorry -
That came out really skewed - the numbers are obvs meant to be set underneath eachother correctly in HTU columns

TeenAndTween Thu 23-Jun-16 13:40:54

1) Are you sure she is meant to be able to do it?
2) Can she do this without the borrowing/exchanging?

I use money. Physical money.
Give her 9 £1 coins and 6 1ps

Say you need 3x£1, 8x10p, 7x1p

She needs to give you the 1ps first.
She hasn't got 7 so would need to 'go to the bank' to change a 10p, but hasn't any of them.
So go to the bank and change a £1 into 10ps
Now go to the bank and change a 10p into 10 1ps

So now she has 8x£1, 9x10p, 16x1p

She gives you 7x1p, 8x10p, 3x £1

What does she have left?

Work with coins first, laid out in columns
Then coins with you showing how it is written
Then written backing up with coins
Then no coins but only talking about them.

But if she can't do this with no exchanging followed by just going to the next door number, don't do the double exchanging question.

Worked for both my DDs, both of whom struggle with maths but are ace at column addition and subtraction.

TeenAndTween Thu 23-Jun-16 13:42:38

So when doing the exchanging with written method, literally cross out the 9 and replace with an 8
make the zero a 10
then cross out the 10 and make it a 9
and turn the 6 to a 16

(not sure from your op whether you know this already or not)

irvineoneohone Thu 23-Jun-16 13:50:27
MadHousewife2 Thu 23-Jun-16 14:30:01

Thanks all - Khan Academy was great - thanks for the recommendation.

I was taught a different method when I was at school in the Dark Ages and didn't want to confuse her - she has been at home last few days and school sent the work home but did not send any instructions about method.

She was fine once she looked at Khan and was reminded of the method - Teen - I'm assuming she's meant to be doing this - she she's top set Y2, is that what they should be working on?

TeenAndTween Thu 23-Jun-16 14:47:37

Mad if the school has sent it home, that's fine! (Sometimes people jump to what they think should be being done without realising the complexities of a question).

irvineoneohone Thu 23-Jun-16 14:47:38

I think what method they use really depend on each school. So you should ask teacher. Our school have calculation method booklet for parents made by teacher.

MadHousewife2 Fri 24-Jun-16 17:10:08

irvine - DD knew which method and recognised it immediately once she saw it on Khan - just needed to go through it again. The calculation method booklet sounds like a great idea - should be standard practice !!

irvineoneohone Fri 24-Jun-16 17:30:37

Yes, it really help parents help their children. They teach everything different from how we learned. Your school may already have one, or suggest to school to make it? Sometimes it takes a while for children to get a hang of stuff, and it makes parents feel confident to help children if they know how they are taught.

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