long multiplcation question regarding method
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long multiplcation question regarding method
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
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
Re: long multiplcation question regarding method
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.
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.
Re: long multiplcation question regarding method
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!
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!
Re: long multiplcation question regarding method
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
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Re: long multiplcation question regarding method
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
Grid method is it.. out of interest do schools teach long multiplication method as well?
SleepyHead
Re: long multiplcation question regarding method
start moving towards that year 6 ish.
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- Posts: 484
- Joined: Thu Oct 18, 2012 10:41 am
Re: long multiplcation question regarding method
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!
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Re: long multiplcation question regarding method
I'm going to quote this next time I'm told it's a stupid method that takes far too long!Guest55 wrote: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!
Re: long multiplcation question regarding method
it's much easier to see where a mistake has been made too (if it has)