How to multiply ANY number by 11 instantly - Free Educational videos for Students in K-12

How to multiply ANY number by 11 instantly - By tecmath

Transcript


00:0-1	Good day . Welcome to Tech Math channel . Really
00:01	, really quick video today for a really simple easy
00:04	Math trick . How to multiply any number by 11
00:07	directly . So sit back , enjoy learn something and
00:10	if you like this video , please remember hit the
00:12	like button and hit the bell as well . If
00:14	you want to get notifications in my next video has
00:17	come out . So Let's go into this . Let's
00:19	directly multiply . So let's go 213 times 11 .
00:26	Now , directly multiplying this , you can get the
00:28	following answer . 2343 . Now look , I'm going
00:34	to show you right now how I did that so
00:36	quickly . Now , just a little thing when we
00:38	do this . By the way , if you're trying
00:39	to do this mentally , you can probably be going
00:42	left or right when you work out your answer .
00:43	If you're trying to go on a piece of paper
00:46	when you do it , I recommend going right to
00:48	left . Okay , so I'm gonna be doing it
00:50	on paper here on the screen . So we're going
00:52	to be our having a look right to left .
00:55	So to get our units part of the answer ,
00:57	we literally look at the units part of our question
00:59	here and we carried across . Okay , so we'll
01:02	carry it down . So three becomes a three down
01:04	here to get the tens part . We're going to
01:07	add these two numbers here . The two right most
01:11	numbers one plus three is equal to four to get
01:16	the hundreds part of the answer . We're going to
01:17	add these two , numbers two plus one is equal
01:20	to three and you get the thousands part of the
01:23	answer . Well this too is just carried down and
01:25	that's how you go about directly multiplying . Oh we'll
01:28	show you why this works a bit later on but
01:30	there is a bit of a complication you can get
01:32	with this just to be aware of . So for
01:34	a second question I'm going to show you where a
01:36	complication can arise . Nothing major . You just have
01:38	to do a little bit of carrying uh say for
01:41	instance , it was a question like this . It
01:43	was a question like 258 times 11 . Okay .
01:50	So the first part of her , that's what we
01:51	do is we just write down this unit's part and
01:53	that's the night . The next thing we do is
01:55	we add these two numbers together . Now you're going
01:57	to see if we do this ? Five plus three
01:59	is equal to 13 . All right , so what's
02:02	going on here ? Do we just put a 13
02:04	down ? And that's not what happens at all ?
02:06	We put the following part down . We just put
02:08	the units part down . Okay ? So and then
02:10	we're gonna carry this one across the next part of
02:13	our answer . So we put the three down and
02:15	we're gonna carry this one across . Two plus five
02:19	is equal to seven plus this one is equal to
02:22	eight . And the last part of our ansa we're
02:24	just going to move the two down here . 2838
02:28	. There's nothing major . Right , Okay . A
02:30	bit more complicated when you're trying to do it in
02:32	your head you just have to watch out for those
02:34	. So what about I'm going to give you a
02:36	couple of too easy ones and then to harder ones
02:39	and then we'll look at why this works . Okay
02:41	. Some examples for you . What about we do
02:43	314 times 11 . What about we do 217 times
02:52	11 . What about we do 383 times 11 .
02:58	And what about we do 275 times 11 . Okay
03:06	. What about you give these to go ? Okay
03:08	, so how did you go with those ? Let's
03:10	go straight into them . These first ones ? Now
03:12	that they're going to be pretty easy , it's going
03:13	to be no carrying evolved , I'm gonna do them
03:16	left to right . Really easy to do in your
03:17	head . So the first part of our answer is
03:19	going to be a 33 plus one is 41 plus
03:23	four is five . And the last part of our
03:25	answers are four , Same with the second question .
03:30	No carrying involved . So two two plus one is
03:33	equal to 31 plus seven is equal to eight .
03:37	And the last part of her answer is the 7
03:39	, 2387 . The third question a bit more difficult
03:43	. Now there will be carrying involved because eight plus
03:45	three is equal 11 . Same down here , I'm
03:47	gonna do this one right to left just to save
03:50	on the aggravation . So the three is gonna go
03:53	down here , we're gonna gonna go eight plus three
03:57	plus three is equal to 11 . So we put
03:58	a one down and we're gonna carry the one ,
04:01	3-plus 8 is equal to 11 Plus . This one
04:04	here is equal to 12 . We put it to
04:06	down and carry the one , The last part of
04:08	her answer . three Plus 1 . Well there we
04:11	go . 4213 . Same deal here . Uh Five
04:16	plus seven is gonna equal 12 . So there will
04:18	be carrying involved . In fact let's us go through
04:20	and do it now . So the fire is gonna
04:22	go down first five plus seven as we said is
04:24	equal to 12 . So the two guys down here
04:26	, we carry the one , two plus seven is
04:29	equal to nine plus one is 10 . Okay ?
04:32	So I'm gonna put a zero down there and a
04:34	one there because the last part of the answer is
04:36	a 22 plus one is equal to three . Now
04:41	I'm going to show you why this works now ,
04:42	but it's a pretty cool trick . Right ? Let's
04:44	see why this works Okay to see what's going on
04:48	here . I reckon we just go and use an
04:50	example . So same would multiply the following two numbers
04:53	here are 352 and we're multiplying this by 11 .
04:59	Yeah , I'm just gonna put the place value of
05:01	each part of these numbers above it . So the
05:04	three is a hundreds there five is a tens part
05:06	of the number and the two is the units for
05:09	our 11 . We have a tens and a units
05:11	part in our answer . We're going to have a
05:13	thousands part of our answer . Hundreds , a tens
05:17	and a units . They're going to show you why
05:19	this is important when we're working on what we're working
05:21	at . So the first thing you're gonna say is
05:23	okay , we can work at the units part of
05:25	our and so we were just riding this number down
05:26	here . Okay . So what's happening ? The only
05:29	way that we can actually get a units number is
05:31	by multiplying a units by units here . Okay .
05:34	And because two times one is going to be too
05:37	, we're just essentially writing this number down here .
05:40	Okay . So that's the units part of her answer
05:44	for the next part of our answer for the tens
05:46	part . Well , there's a couple of things that
05:48	can occur . There's two different ways we can get
05:50	tens , we could go units times tens here or
05:53	tens times units here , both of them giving us
05:55	tens answers and then we have to add those two
05:58	answers together . Now , what do we have going
06:00	on here ? We have a five times a one
06:02	or two times to one . Now look , that's
06:04	pretty redundant . Multiplying by one . It doesn't really
06:06	do very much . Doesn't change our answer . So
06:09	all we're going to be really doing is just adding
06:11	are five and to hear five plus two is equal
06:14	to seven . Yeah , you're probably gonna see what's
06:17	going on now . Right ? How do we go
06:19	about getting the hundreds part of a ransom where you
06:21	could have hundreds times units or you can have tens
06:24	times tens , but once again you're multiplying by ones
06:27	over here . So really all we're worried about is
06:28	what's happening with these numbers over here . And we're
06:30	going to add those five plus three Is equal to
06:34	eight . The last part of our answer . Well
06:37	, the only way we can get a thousands part
06:39	is by multiplying the two biggest party . We have
06:42	the tens by the hundreds and this would give us
06:45	thousands answer re multiplied , but once again multiplied by
06:49	one , doesn't change the R number . So we
06:52	just write down the three , 3872 . And that's
06:56	why that trick works OK . Anyway , hopefully you
06:59	like this are particular trick and like I said ,
07:01	if you do hit the like button and subscribe and
07:03	put on the notifications as well . Once again ,
07:06	a really , really big shout out by the way
07:08	to my patrons as well as Gary who donated some
07:11	money as well to the tech Math channel . Look
07:13	, your support is greatly appreciated Anyway . Any videos
07:18	you like me to make make sure you put in
07:19	the comments are , we'll see you next time .
07:22	Thanks for watching . Bye .

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