# Talk

## TEACHERS!!!! sorry for shouting...but can anyone help my 9yr old ds1 with long multiplication?

(20 Posts)
cutekids Sat 27-Sep-08 10:14:35

If anyone knows how they do it now, please,please can you help us!!!?!!!

cece Sat 27-Sep-08 10:16:16

is he doing the grid method?

cutekids Sat 27-Sep-08 10:22:17

cece,i really don't know....! I don't really get maths myself.
he's just got a sheet with:
"Leila bought 19 videos at £17 each"???etc.
and a couple of sums:"19 x 24="etc.

MamaChris Sat 27-Sep-08 10:27:01

Not a teacher, but, in the old old days when I was at school, you'd write it out like:

19
x24
----

Then the first line you'd do 4x19, so you'd have

19
x24
---
76

And the next line you put a 0 at the end, so you have

19
x24
---
76
0

then fill in 2x19 behind that

19
x24
---
76
380
---

Then add the last two lines

19
x24
---
76
380+
---
456

The idea is that 19x24 is just 19x4 + 19x20, and that 19x20 is easy, because it's just 19x2 with a 0 on the end.

Does that help at all?

cece Sat 27-Sep-08 10:27:22

OK 19 x 17.

Ask him if he knows how to draw the grid.

Then partition the 19 into 10 and 9. Put that along the top of the grid.

Then partition the 17 into 10 and 7. Put that down the side of the grid.

Then do the four times tables and fill in your grid.

10 x 10 = 100
10 x 9 = 90
10 x 7 = 70
7 x 9 = 63

then add up the totals; 100+90+70+63=323

bamboostalks Sat 27-Sep-08 10:29:00

Piss poor there is no example. Ask him which method he is being taught. If grid, then partition numbers out so 10 x 10 =100, 10 x 7=70, 10x 9=90, 9x7=63 and then add up all the answers.

MamaChris Sat 27-Sep-08 10:29:18

oops, all the spaces got lost on that. those sums should look like (with _ indicating a space)

_19
x24
----

Then the first line you'd do 4x19, so you'd have

19
x24
---
76

And the next line you put a 0 at the end, so you have

19
x24
---
_76
_
0

then fill in 2x19 behind that

19
x24
---
76
380
---

Then add the last two lines

19
x24
---
76
380+
---
456

TheCheeseAlarm Sat 27-Sep-08 10:29:22

If they are all 19x something then they don't want him to be doing long multiplication.

They are working on multiplying by 20 and then subtracting.

So for the first one.

17x2=34
34x10=340

Which gives you 17x20

Then 340-17=323 gives you the answer

So 19x24

20x24=2x24x10=480

480-24=456

so 19x24=456

It's about using the easier calculations you know, such as x2 and x10 to work out harder calculations.

bamboostalks Sat 27-Sep-08 10:29:48

Cece much clearer, I am better in front of a class!!

SmugColditz Sat 27-Sep-08 10:30:28

You know, I passed gcse maths and still can't do this, I'm shocked they teach it at nine!

MamaChris Sat 27-Sep-08 10:30:37

Argh! And now they've come out as underlines. Plus it looks like this isn't the way kids do it anymore (never heard of grid method). Ignore all my ramblings.

cutekids Sat 27-Sep-08 10:33:19

wow! thanks for all the examples...i'm gonna have to sift through which ones make sense to him.no,they aren't all 19xsomething...it's just that i happened to pick those 2 out!
i'll get back to you when i've figured things out...!

shivermetimbers Sat 27-Sep-08 10:33:46

19x24 would be like this.

x 10 9

20 200 180 = 380

4 40 36 = 76
-----------
456

this would be in a grid but gant draw one.

shivermetimbers Sat 27-Sep-08 10:35:09

sorry its gone all wonky makes no sense now

cece Sat 27-Sep-08 10:49:46

On here there is a powerpoint presentation to show you the grid method.

AbbeyA Sat 27-Sep-08 10:58:37

If every sum is x19 then there is no need for long multiplication you need to multiply by 20 and subtract as explained by TheCheeseAlarm.
19x24
20x24=480 480-24=456
19x24=456

I should ask ds which method he was told to do. Grid is the easiest. I am not clever enough to draw it on here.
20 and 4 along the top
10 and 9 down the side
Multiply the separate parts and add up for the total.

AbbeyA Sat 27-Sep-08 11:01:45

Sorry - I have just read that they weren't all 19x
He could still show initiative by doing those ones by the quick method!
e.g.if x21 do 20x and addthe 1x

schneebly Sat 27-Sep-08 11:02:26

Ooh the grid method rocks!

Just been looking at the powerpoint on long division too - just started a primary teaching degree and will need to know all this!

cece Sat 27-Sep-08 11:06:12

Good isn't it?

AbbeyA Sat 27-Sep-08 11:39:13

If any adult needs help to see how to do a certain maths problem the BBC Skillswise site is good.this page

The advantage of this site is that it gives all methods and also shows the traditional column method.

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