YR 5 Multiplication help neeed please

[isitspringyet]

Have a 10 yr old and need help explaining sums i.e. 7 x 21, 15 x 4. I am hopeless in maths need to teach him to do it with confidence. Please help anyone who can explain it easily as have googled already and still don't get it myself. Thanks

[Goingspare]

A friend has recommended this book to me for helping with maths. Haven't got it myself yet though.

[witchwithallthetrimmings]

There are lots of ways to explain this but I think the key is to build on what he has learnt at school. Does he know his times tables? Does he know what multiplication is (i.e that 7 x 21 = 21 + 21 + 21 + 21 + 21 + 21 + 21)?

[hatchypom]

I don't know how its taught at school these days, but i think you do 7x1 + 7x20 write them underneath each other gives you 147

15x4 is 10x4 and 5x4 total is 60

I think they call this chunking ? I always thought it was long multiplication

Key is knowing timestables

[nailonthehead]

DD year 5 says she would do 7x2 = 14 so 7x 20= 140 add 1x7 = 147.

(10 x 4) equals 40 add (5x4)equals 20 = 60.

The first bit is place value so understanding if you know 7x2 you also know 7x20 or 7x200 etc.The other bit is chunking.

She has done lots of table grids this year to check she is solid on the times tables. She likes tutpup as well.

[witchwithallthetrimmings]

chunking is division. I think they use somehting called the grid method for multipication. I'll see if I can explain it.

First you need to understand that you can think of any multipication sum as making a grid or rectangle of dots. So 3 x 2 is a rectangle with 3 rows and 2 coloumns. Count each element and we get 6 = 3 x 2. We can do this for any sum including 7 x 21.

so think of this grid as having 21 rows and 7 columns. In the first 10 rows there are 70 dots (10 x7)) In the next 10 rows there must also be 70 dots. This leaves one row left with 7 dots. Thus the number of dots in total is 70 + 70 + 7 = 140+7 = 147

The key is to split the rectangle up into sums that you know. Thus knowing your times table is crucial.

Thinking of the sums in this way may seem overly cumbersome at first but it really does help in getting them to understand what mmulitiplication is about

[Pozzled]

Yes, grid method for multiplication.

A couple of websites to try-

www.primaryresources.co.uk/maths/mathsC2d.htm

This is more aimed at teachers but if you look for 'Grid method TU xU' you'll find some worksheets that he could try, and it shows you how to set them out.

nationalstrategies.standards.dcsf.gov.uk/node/47783

This is a government program, you can make up your own sums by clicking on up/down arrows at the bottom, and it will then show you what happens on the grid.

However, I would say best thing is to ask the teacher to demonstrate the method to you, it should only take a few minutes and it's easier to explain to someone in person.

[isitspringyet]

Thanks so much everyone for your advice and support. Mumsnet is such a great resource - better than google!!
He regularly goes on to Tutput and my parents explained the old way of doiong to him which I have to say I find easier too.
Definately going to check out the book and the websites. Thanks again everyone for taking time out to reply.

[3point14]

Don't kids chant their table endlessly day after day to learn them off by heart these days ?