Fast Math Tricks - multiplication of two and three digit numbers - Free Educational videos for Students in K-12

Fast Math Tricks - multiplication of two and three digit numbers - By tecmath

Transcript


00:0-1	get a welcome to the Tech Math channel . What
00:02	we're going to be having a look at this video
00:03	is a way of multiplying two and three digit numbers
00:06	together are using this rainbow multiplication method that I've had
00:09	a look at in a previous video . So let's
00:12	have a look at this . Okay , so say
00:15	we were asked to multiply a number such as 121
00:20	times 23 . Now , the way that we could
00:24	do this using this particular method is as follows .
00:27	So first off to get the first part of our
00:31	answer , what we do is we multiply the first
00:33	digits in our numbers here , so one times two
00:36	is two . Okay , So we're gonna have to
00:42	, then what we're going to have is to middle
00:44	digits , which we're gonna come back to it a
00:46	little bit . I'll show you how to work this
00:48	out , but we're gonna go straight to working on
00:49	our last digit . The way that we work this
00:51	out is multiplying the last digits here . So one
00:54	times three is three . Yeah , so far this
00:59	is much like this other method of multiplication , where
01:01	we had a look at where we're multiplying two and
01:03	two digit numbers together . But this is a slight
01:06	tweak on it . Now what we do now is
01:09	we're going to work out this particular number here .
01:12	What we do is we do this thing called Rainbow
01:14	model location . We're going to multiply this number by
01:17	this number and this number by this number . You
01:21	can see what we call it . Rainbow modification .
01:23	Yeah . We're going to add our answers together .
01:25	It will give us the number that's going to go
01:26	in here . Okay , so one times two is
01:29	to and two times 3 is six . We're going
01:34	to add these answers together to get and I'd Okay
01:39	, so eight is going to go in here .
01:42	All right , to get the this number here .
01:45	The next part of our answer . We're going to
01:47	do this rainbow modification . They do it underneath here
01:49	, but I'm going to move The actual these parts
01:52	across one . So 2 times two and three times
01:57	what ? Okay , so two times two is four
02:01	. We're going to add that 23 times one ,
02:04	which is three , so three plus four equals seven
02:08	. So answer Is 2,783 , which is the correct
02:14	answer . So that's a really , really cool method
02:15	. Yeah . Uh it's not too confusing . I
02:18	don't think there's any bit there that you won't be
02:20	able to remember , but hey , let's see .
02:23	I'll tell you what , I'll go through one more
02:24	example . They don't give you a bunch of wants
02:26	to do for yourself and see how you go with
02:28	it . In fact , I'm gonna leave some of
02:29	the harder ones I think for you . Okay .
02:31	Uh What about we go through one more of these
02:34	? Um 242 . And we multiply this by 32
02:41	. Okay . So to get this first part of
02:44	Iran to what do we do ? We multiply these
02:47	three times two is six . Okay I'm going to
02:51	put this in a red pen to six . Okay
02:54	. To 3 to 6 . We leave two spaces
02:56	12 Okay then what we do is we get the
03:00	last part of the answer two times two which was
03:02	four . Okay so we're doing pretty well so far
03:05	. You're right . Okay let's get this digit here
03:09	. So what we did is we do this rainbow
03:11	multiplication thing . Yeah , this is three times to
03:15	we're going to add that to two times four .
03:19	So three times two is six and we're going to
03:21	add at the two times four which is eight ,
03:25	So six plus 8 equals 14 . Yeah , I'm
03:29	gonna put the four down in here . But what
03:33	I'm gonna do is I'm gonna put the world because
03:34	we're gonna Be carrying that into our next part of
03:37	our answer here . So the 14 , we only
03:39	put the four part of it down and we're gonna
03:40	put the wonders there just to remind us that we're
03:42	going to be putting it into here . So let's
03:45	do the next part of our rainbow model location three
03:48	Times four , which is 12 . We're going to
03:51	be addie To two times 2 which is four .
03:56	So we add those , we get 16 , 16
03:59	plus one here , We get the answer of 17
04:02	. So that's going to become a seven and I'm
04:04	going to move this one across into here . So
04:06	what are we going to do ? We are going
04:08	to add it to the six here , so the
04:10	six is going to become a seven . Okay .
04:14	Where we added that one in ? So my answer
04:16	is 7744 . Okay . So hopefully uh , that
04:24	worked out for you . Okay . What are able
04:26	to give you a couple of hard examples of these
04:29	are the ones these aren't that hard ? Okay .
04:31	It's the same exact same method as long as you
04:33	can remember where you have to , you know ,
04:37	Place things and carry things and that sort of deal
04:39	. You'll be pretty right . So I'll give you
04:41	a nice easy one to start off and then I'll
04:43	give you the hard one . Okay ? So what
04:44	about 122 Times 32 . That will be the first
04:51	one I'll get you to do . And then I'm
04:54	going to get you to do 153 And we're going
04:59	to multiply that by 61 . Okay , pause the
05:03	video , give them a go and I'll see you
05:06	back here in a minute . Okay . Hopefully you've
05:09	done those and let's check how you went on those
05:11	. So Okay . One times three is three .
05:18	Two spaces , boom and boom and two times 32
05:23	times two is four . Okay . So we're doing
05:26	pretty well so far . Hopefully you're pretty good so
05:29	far . Now what we do is we do this
05:31	rainbow multiplication . So we're gonna be getting six and
05:34	adding this to four , which is 10 . So
05:37	I'm gonna put a zero there in a one there
05:39	. We're going to be putting it here , we're
05:42	going to go three times two which is six to
05:44	that , we're going to add to six and two
05:47	is eight plus . This one here is nine .
05:49	So did you get the answer to ? 3904 ?
05:52	If you did . Congratulations if he didn't . Well
05:55	you just have a quick look over how I did
05:57	it there and and see where you made a mistake
05:59	. Fix it up . Okay . Okay um let's
06:03	go this last one here . So one time six
06:05	or 6 couple of spices , one times 3 is
06:11	a three . Okay now let's do this rainbow multiplication
06:15	here . Okay so we're gonna go three times six
06:17	which is 18 and one times five which is 5
06:22	18 plus five is 23 . Okay so I'll put
06:26	the three there and I'm gonna put my little two
06:27	up there . six times 5 is 30 , 31
06:34	Plus two is 33 . So that three is going
06:37	there and another three is gonna have to be added
06:39	to our six year . So this is going to
06:41	become a nine . Okay ? So my answer is
06:45	9,333 . So hopefully you really , really get the
06:52	hang of that method . It's not a bad method
06:53	. Tell us what you think about that . Tell
06:58	your friends . Show everybody . All right , anyway
07:01	, Thanks for watching . See you next time .
07:03	Bye .

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Fast Math Tricks - multiplication of two and three digit numbers is a free educational video by tecmath.

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