long multiplcation question regarding method

[SleepyHead]

Hi ForumMembers.. I am trying to teach DC long multiplication, school teach the box method which I find mind boggling

If this was the question, how would you teach it, here's my approach. Please comment/correct ... is there an easier way.

Feedback greatly appreciated.

213
45 *
------
0

first cover the 5, then put a zero in, the units coloum

then do 4 * 3 = 12 , put the 2 in carry the 1

213
45 *
------
20
------
1

then do 4 * 1 = 4 (add the 1) = 5

213
45 *
------
520
------
1

now do 2 * 4 = 8

213
45 *
------
8520
------
1

now do the units side

5 * 3 = 15 put the 5 in carry the 1

213
45 *
------
8520
5
--------

then do 5 * 1 = 5 add 1 = 6

213
45 *
------
8520
65
--------

then do 5 * 2 = 10


213
45 *
------
8520
1065
--------


now add together

9585 total

Thanks
SleepyHead

[moved]

I would teach a grid method as it is useful for multiplying algebra in ks3 and 4. If. A child used another form of algorithm confidently I would be happy for him/her to use it.

Cannot reproduce here, but put 200, 10 and three across the top and 40 and 5 down the sides.

2 x 4 = 8 then add the zeros, in this case 000, etc.

I have used this method with lower attainers at gcse who have never previously grasped long multiplication.

(x + 2)(x + 3)

x and 2 across the top, x and 3 down the side.

Some primary children don't like the method, because they have already learnt the algorithm, if they are happy using it then fine with me.

[Okanagan]

Asked ds how he'd work out 213*45

add a 0 -> 2130 is 213*10
half it -> 1065 is 213 *5
add another zero -> 10650 is 213*50
subtract the 1065 from the 10650.

Doesn't work as well for all numbers of course!

[yoyo123]

The grid method is surprisingly handy once you get used to it. It makes it easy to spot mistakes, even though I was brought up on "proper" long multiplication I like it

[SleepyHead]

Thanks everyone for your replies. That helps clears things up.

Grid method is it.. out of interest do schools teach long multiplication method as well?
SleepyHead

[yoyo123]

start moving towards that year 6 ish.

[SleepyHead]

thank you.

[Guest55]

You don't ever need more than the grid method as we build on that in Secondary and we use it right through GCSE and A level algebra!

[wonderwoman]

You don't ever need more than the grid method as we build on that in Secondary and we use it right through GCSE and A level algebra!

I'm going to quote this next time I'm told it's a stupid method that takes far too long!

[penguin]

it's much easier to see where a mistake has been made too (if it has)