Fast Maths Calculation - Multiply four digit numbers FAST! - Free Educational videos for Students in K-12

Fast Maths Calculation - Multiply four digit numbers FAST! - By tecmath

Transcript


00:01	Good day and welcome to the Tech Math channel .
00:03	What we're going to be having a look at today
00:04	is how to multiply four digit numbers . So to
00:07	four digit numbers together and we're going to start very
00:10	, very easy on this . But before we start
00:12	on this . So I think it would really be
00:13	recommended if you haven't done this already . You're going
00:16	to look at my videos on how to multiply two
00:18	digit numbers and how to multiply to three digit numbers
00:21	together . This will probably make this video a whole
00:23	lot easier if you do that . Because a lot
00:25	of the ideas we looked at there are the same
00:27	as the ideas we're going to look at in this
00:29	video . So I'll put these links up hopefully there
00:32	if they don't write some comment and remind , you
00:34	know those . But I should remember that Anyway .
00:38	Let's go there . Let's see how fast you can
00:39	do this particular question . Then I'll tell you what
00:42	we'll start off with a nice easy one . What
00:44	about This ? four digit number . 1000 and 12
00:50	at times this , I'll give myself a bit of
00:52	space By 1123 . I'll give you five seconds to
00:58	get the answer on that one , And you go
01:04	on that if you got the answer , if you
01:06	got the answer of 1,136,476 , you did really ,
01:11	really well , but if you didn't and you're still
01:15	trying to work it out , let me show you
01:16	a little trick on how you might get a bit
01:17	faster . We're doing these , you might not be
01:19	able to give them five seconds , but you're still
01:21	going to get a whole lot faster than you're probably
01:22	used to working it out . Okay , so this
01:27	is how I would work out this particular equation .
01:29	Okay , so first off , we want to get
01:31	we're going to work by getting the answer in this
01:34	direction . So I'm going to get the last answer
01:37	, the last number of this answer and then right
01:39	up to the first number , I'll show you how
01:40	I do this . Two times three There's six .
01:43	I'm going to multiply these two numbers first together ,
01:45	two times three . His six . That's the very
01:48	last number of our answer . Okay , the next
01:52	thing going to solve because I'm going to get the
01:54	next number coming on here . Okay . And the
01:56	way we do this is to multiply this number by
01:58	this number and this number by this number . Okay
02:02	, so one times three is 32 times two is
02:05	four and if I add these together , get the
02:08	answer of seven . Pretty cool . Right . Okay
02:12	, let's go on to the next part of our
02:14	answer . We're going to get this next number here
02:16	. Okay , So we're gonna multiply these numbers .
02:19	These numbers and these numbers , you might see a
02:21	bit of a pattern here . Okay . Okay ,
02:25	so two times one is two , Nothing Times three
02:28	is nothing and one times two is to add all
02:31	these together . You get the answer before too ,
02:36	Plus two is 4 is the next part of the
02:39	answer . All right , now , this is probably
02:43	the hardest calculation in the whole entire some we've got
02:45	now , because I want to multiply this number and
02:48	this number , this number in this number , this
02:51	number and this number This number and this number you're
02:55	getting a bit of a symmetrical thing going here where
02:57	it's almost going from one corner to the opposite corner
02:59	. Okay , we're getting this sort of thing going
03:01	. So one time three it's three nothing times two
03:05	is nothing . One times one is 12 times one
03:09	is to add all these together . We get the
03:12	answer is six . Okay , Next one . Now
03:18	we're going to actually working on this next number .
03:20	And what we're going to do is now we've been
03:22	moving in this direction . We're actually going to start
03:23	working now on this side . Okay , so two
03:30	times one is 21 times one is one , add
03:33	these together , we get three . The next numbers
03:35	, you might be able to guess which ones we're
03:37	going to multiply these ones and these ones one times
03:39	one is one nothing times one . Nothing times one
03:42	is nothing . We have these together . We get
03:44	the answer are one and the very last of all
03:46	, what we're going to multiply is we're going to
03:48	multiply these two numbers One and one or one times
03:52	one can get the answer of one . So there's
03:54	our answer . 1,136,476 . And especially if you've watched
04:00	those other videos , you're probably really , really getting
04:02	this pattern of how this is working now . Okay
04:05	. And it's a really , really easy pattern to
04:08	get when you work it out . Okay , So
04:13	, so let's move on to one more example ,
04:15	and then I reckon you could probably go on your
04:16	own and then give these a bit of a go
04:17	. So I'll get rid of these . And I
04:19	put one more example up on my little pad here
04:22	. What about we go this one . Speaking in
04:24	the eyes of symmetry , we'll go 1234 by 4321
04:30	will multiply these two numbers together . What do we
04:32	get ? So I'm going to do this really ,
04:34	really , I was going to do it quickly ,
04:36	but I might actually do it at a pace .
04:38	You might be able to give it a go to
04:40	. In fact I recommend you pause for me a
04:41	minute and then we'll go through the answer together .
04:43	So pause . All right now let's go through the
04:46	answer . So hopefully this is what you did one
04:51	times 4 . It's four three times one and four
04:55	times 23 plus eight is 11 now because we actually
04:59	can't write down 11 were out there one digit ,
05:01	we write the one from the 11th and that's the
05:02	second one and we carry one across . Okay ,
05:07	so hopefully you good with that then what we do
05:09	is we multiply these ones are two and one ,
05:12	two times one is 23 times two is six .
05:15	Four times three is 12 together . They add up
05:18	to 20 . We add this little one here which
05:20	is 21 and I'm going to Put that in there
05:23	and we carry the two across . Next . What
05:26	we do four times 4 , 16 , 3 times
05:30	three is 92 times two is 12 . 1 times
05:33	one is one . You might want to write those
05:35	down , But together those guys had up to 30
05:38	. Okay , that's probably the hardest calculation the entire
05:40	bit and then you add this little to on .
05:42	So That's going to be 30 to carry the three
05:45	across . Okay , now we're on moving onto this
05:48	side now . Okay , so three times 4 ,
05:51	12 , 2 times three is 62 times one is
05:54	two together . They add up to 20 At the
05:57	three on 23 . Okay , let's put the two
06:01	down there to carry it . Next , we've got
06:03	to time Sport which is 81 times three which is
06:06	three together . These add up to 11 plus two
06:09	is 13 carry the one across four times one is
06:13	four plus one is five . What a big answer
06:16	we got there is 5,332,000 100 And 14 . So
06:23	hopefully you went pretty good with this . This is
06:24	a little bit slightly a modification of what some other
06:28	types of our questions they get , you're doing these
06:30	on other videos , it's a little bit bigger .
06:33	I tend to like to put the actual carrying numbers
06:35	down here . I've noticed a few people don't do
06:37	that , but it really , really helps rather than
06:39	trying to cross things out later on . I think
06:41	it's a lot easier way of doing it . Let
06:43	us know anyway , tell us what you think ,
06:45	if you've seen a few of the other methods anyway
06:47	. I hope you get the hang of that really
06:49	, really quick . See you next time .

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