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How would your year 2 child subtract 74 from 90?

42 replies

janinlondon · 28/11/2006 12:00

Title says it all really. What method is your school using for this kind of simple subtraction?

OP posts:
Enid · 28/11/2006 12:02


she'd panic, have no idea and then take a wild guess

she'd probably say 2?

god she really IS behind

southeastastra · 28/11/2006 12:04

i'd line up 90 smarties take away 16 and probably open a bottle of vodka!

porpoise · 28/11/2006 12:09

he'd probably do some kind of rounding up/rounding down kind of thing.
So 90 minus 70 minus 4...
and he'd do it all in his head.
ALL the maths he does is mental maths.
His older brother (yr 4) is only just starting to do stuff on paper.
VERY different to the maths I was taught as a child - they both roll their eyes at me when I try to explain how I'd do it!

Hallgerda · 28/11/2006 12:14

Draw a number line with the numbers.
74 90

Now put in the next "ten" above the smaller number, and fill in the differences (on nice curvy lines which I can't do properly here)

74 80 90

6 10

Now add up your differences, and you get 16.

That's the official version. It's conceptually easier than column subtraction, but really does exactly the same.

But then again, DS3 worked out that he could split into tens and units:

90-70 = 20
0-4 = -4

20 -4 + 16.

As it worked and negative numbers didn't seem to worry him I let him use that one!

batters · 28/11/2006 12:14

This reply has been deleted

Message withdrawn at poster's request.

janinlondon · 28/11/2006 12:24

Reaching for the vodka as I type number lines or squares any more. Mental maths where possible (well it isn't, at least for DD!!!). Mental maths barely possible for me....

OP posts:
gladbag · 28/11/2006 12:26

I haven't taught Y2 for a few years, so am rusty, but....

I'd expect a very able Y2 to do it mentally by 'finding the difference', so saying "74 to 84 is 10, then 6 more to 90, so 16".

A child less sure mentally could use an 'empty number line', so draw a line, put 74 at one end and 90 at the other, then find the difference in the same way, but writing down the jumps, probably going backwards, 90 to 80 is 10, 80 to 74 is 6, so 16.

Or they might split the 74 into 70 and 4, and write
90 - 70 = 20
20 - 4 = 16

I wouldn't expect them to use column subtraction.

nearlythree · 28/11/2006 12:28

Apparently the DofE has a 'consultation' about the methods used for maths. The result is expected to be a foregone conclusion - a return to using columns (much like phonics has made a comeback).

foxinsocks · 28/11/2006 12:31

my yr 2 child wouldn't have a clue if I just asked her off the top of her head

I think they use number squares but I think she would definitely battle even using one of those

janinlondon · 28/11/2006 12:33

Nearlythree - they are using columns to do complex addition, but I worried that showing her column subtraction might confuse her - all the borrowing etc?

OP posts:
PandaG · 28/11/2006 12:34

Ds would do it as Glad bag suggested - but he would probably say well 74 to 80 = 6, and 80 to 90 = 10 so 6+10 = 16. I had a heart attack when I realised he didn't use columns, as that was how I expected him to do it, but he understands how his method works.

foxinsocks · 28/11/2006 12:35

they def use number squares at dd's school - she has no idea of the column method at all

nearlythree · 28/11/2006 12:51

I expect that trying to use columns for a child who is taught something very different in school would be confusing. My dd1 is only in reception so I'm hoping that columns will have made their comeback by the time she is taught this type of calculation. I struggle with arithmetic and have tried the current ways that children are taught and really found them hard. Dd1 seems to have her father's gift for numbers so should fare better, but I have heard that the problems tend to show up worse in secondary school. Because children are required to show their workings, and there are so many calculations to make, very often small errors occur which then throw out the whole answer. Put simply, columns are more reliable.

My dad used to work as a sales rep which required good number skills. He now volunteers as a mentor to young people with behaviour problems, but in terms of their learning can only help with reading as the maths methods they use make no sense to him. He can add up in his head in a flash and it saddens me that these young men are struggling with something that could be made so much simpler for them.

Amanda1 · 28/11/2006 12:53

Message withdrawn

poppyknot · 28/11/2006 12:53

We have been introduced to 'horizontal subtraction'at a parent night. We were a bit confused and the teacher wasn't entirely convinced herslf.

90 - 70 = 20

0 - 4 can't do so 4 - 0 = 4

Then do subtraction 20 - 4 = 16

NB If the units of the larger number are larger ie 96 - 72 then 6 - 2 = 4 and you ADD that to the twenty. It's having an ADD sum in the middle of a subtraction that seems to be a bit baffling but presumably they will just learn the method and get the understanding later..

janinlondon · 28/11/2006 12:56

Thanks so much everyone - this is really useful.

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LadyMuck · 28/11/2006 12:57

OK - I'm going to show how thick I really am: if schools aren't teaching subtraction via column method anymore then how do they do sums such as 956,375-635,964? I can't think that I know of any other way (other than estimation).

edam · 28/11/2006 12:58

Blimey. When I was at school I did this sort of sum as mental arithmetic by 90 - 70 - 4 kind of thing but it was Looked Down Upon and I had to write it all down in columns. Am v. of children who are allow to do it my way!

Olihan · 28/11/2006 13:00

The idea of all these different methods came about as part of the Numercay Strategy, to give children a wider range of methods to use, so that they could find a strategy that worked for them. It's supposed to make life easier for the children as not all children learn by writing numbers in columns.

Having said that, the Numeracy Strategy is widely recognised as failing to improve standards (no surprises there!) so I'm sure we will see a change back towards columns and 'traditional' pencil and paper methods.

Olihan · 28/11/2006 13:02

LM, they do do column subtraction, but not until mauch later on - Y5-6 I think. It definitely makes a comeback in Secondary school because the Numeracy Strategy is written for Primary schools.

batters · 28/11/2006 13:02

This reply has been deleted

Message withdrawn at poster's request.

throckenholt · 28/11/2006 13:09

I think it is supposed to give them a feel for numbers - so you deal with the big numbers first - to get to the right ball park, and then go back and sort out the left over bits.

Tricky for us old fogies to get our head around the different way of thinking - which means it is not easy for use to help them when they get stuck.

If it gives the kids a feel for what the answer ought to be then it is a good thing, though.

I remember a few years ago doing a practical with some first year undergrads - they had to work out the wind speed at a given height - most of them came up with the right number of about 30 mph - one group had something that was about 3 times the speed of light (of which they were totally unaware). They wrote it up on the board along with all the rest - and even when questioned about it they were perfectly happy with their answer. Thus proving that they actually had no idea and no deel for what they were doing.

janinlondon · 28/11/2006 13:10

Think you're right Batters....but vodka is less detectable in the office.

OP posts:
LadyMuck · 28/11/2006 13:11

Thanks - at least I'll be some use when Year 5 comes round. What other shocks are there going to be? ds1 has started learning times tables so they must still be the in thing. He hasn't started division yet though.

throckenholt · 28/11/2006 13:12

oops - feel not deel

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