5 Fast Math Tricks for Multiplication - Mental Math - Free Educational videos for Students in K-12

5 Fast Math Tricks for Multiplication - Mental Math - By tecmath

Transcript


00:0-1	Good day . Welcome to tech Math channel . A
00:02	whole bunch of fast multiplication tricks right now . I
00:05	hope you enjoy them . So the first trick we're
00:07	going to have a look at is multiplying by 11
00:09	. So say for instance , 11 multiplied by 134
00:15	. This is equal to his followers . The first
00:17	digit we just put the first digit down here .
00:20	So it's a one . The next digit we add
00:22	these two guys , one plus three is equal to
00:24	four . The next digit we had these two guys
00:27	, three plus four is equal to seven . And
00:30	the last digit while we just right at the last
00:32	digit , which is a four . Our answer .
00:34	1474 . What about another one of those ? Okay
00:39	, what about 11 ? Multiplied by 2471 . Okay
00:46	, let's go through . First digit is going to
00:49	be a to hear the next digit we had these
00:51	two guys together . Two plus four is equal to
00:54	six . The next digit we add these guys seven
00:57	plus four is equal to 11 . So what we're
01:00	going to do is we're going to put one of
01:02	the parts of our 11 down here . What we're
01:03	going to carry that next one across here . So
01:06	the six is going to become plus one equal to
01:10	a seven . The next digit , seven plus one
01:13	is equal to eight And the last digit is the
01:15	one here . So 11 times 2471 is equal to
01:20	27181 . All right , let's get on to the
01:24	second trick to the second trick is multiplying by teen
01:27	numbers such as 13 times 12 . How we do
01:31	this is as follows . So we're going to look
01:34	at the end two digits here . Okay . And
01:36	then what we're going to do is we're gonna get
01:38	one of these are two for instance here and we're
01:40	gonna add it to this . 13 so 13 plus
01:42	two is equal to 15 . That's the first part
01:46	of our answer for the second part of our answer
01:48	for the units part here we are just going to
01:51	multiply these two digits , so three times two is
01:54	equal to six , so 13 times 12 is equal
01:58	to 156 . What about to give another one of
02:01	those who go ? So what about we do a
02:03	bit of a harder one now , what about we
02:05	do 15 multiplied by 19 and we'll see what that
02:09	equals . Okay , so we have the units parts
02:12	here . The five and the 9 15 plus nine
02:15	is equal to 24 . Now , what we're going
02:18	to do is five times 95 times nine is equal
02:22	to 45 . So the five part of the 45
02:25	is going to go here , but the four is
02:27	going to be carried across . Four plus four is
02:30	equal to eight . Our answer is 285 . So
02:35	that's a nice little trick to write . And it
02:36	works for any number in its teens . Up to
02:39	20 . Okay , so let's look at the next
02:41	modification trick . Okay , What about now ? For
02:43	this next trick ? We'll look at multiplying bigger two
02:45	digit numbers and then we'll have a look at multiplying
02:48	three digit numbers with one another . Let's start with
02:50	a nice easy 1 , 23 . Multiplied by 12
02:54	. Now to get the units part of our answer
02:57	, we're going to look at the units part of
02:58	our question and we're gonna multiply them . So three
03:01	times two is equal to six to get the next
03:04	part of our answer . We're going to do a
03:06	bit of rainbow multiplication and addition . I'll show you
03:09	what I mean by this . So we get this
03:10	nice rainbow shape here . Okay , we have three
03:13	times one which is equal to three and two times
03:16	two , which is equal to four . And we're
03:18	going to add those two together . Three plus four
03:21	is equal to seven . That's the 10th part of
03:23	our answer . And then finally to get the hundreds
03:25	part of our answer . We're just going to multiply
03:27	the hens party . So two times one is equal
03:30	to two . Our answer . 276 . What about
03:34	to do a harder one of those . What about
03:36	we do 14 times 23 . Not going too hard
03:40	yet . I'm going to keep these fairly simple today
03:42	. So let's get the units part first four times
03:46	three is equal to 12 . You got this idea
03:49	, We're going to put the two part down and
03:50	then put the one up here to be carried across
03:53	. We have four times two which is equal to
03:56	aid into this . I'm going to add three .
03:59	Okay , one times three is equal to three .
04:01	So adding these guys together , we get 11 ,
04:04	11 plus this one here . This is going to
04:07	be 12 . I'm going to put the two there
04:09	and carry the one finally to get the last part
04:12	of our answer one times two is equal to two
04:15	plus this one here . Our answer is 322 .
04:21	Hey , that's not too bad . Right . What
04:23	about now ? We do the bigger ones . So
04:25	this is how I go through now and multiply bigger
04:27	numbers . Say I had 132 and I wanted to
04:31	multiply by 214 and I want to do this directly
04:36	and I want to be having a whole string of
04:38	things here . I want to multiply this guy out
04:40	directly now , it's pretty simple . And this is
04:42	the pattern we're going to follow . You're going to
04:43	see this , we're gonna multiply these guys , then
04:46	these guys , then these guys , then this and
04:49	then this , you'll see this pattern as I go
04:52	along . So first off , two times four is
04:55	equal to eight . The next one we're going to
04:58	multiply these two guys and we're gonna add our results
05:00	three times four , which is 12 plus one times
05:03	two which is 2 , 12 plus two is equal
05:07	to 14 . I'm going to put a one down
05:09	there to carry the next one . I'm going to
05:11	be doing . These guys are going to have this
05:13	star pattern once again , one times 43 times one
05:16	and two times 24 times one is equal to four
05:20	plus three plus four . Four plus three plus four
05:24	is equal to 11 plus . This one here is
05:27	12 . Put the two down , carry the one
05:30	. You've probably got this next part . We're gonna
05:31	be going the star now across here , but now
05:33	we've moved across the hundreds and tens , one times
05:36	one and three plus two . Well , that's one
05:39	plus six , which is equal to seven plus .
05:41	This one here is equal to eight . And finally
05:45	, we're just going to multiply the two hundred's ones
05:46	here . One times two is equal to to our
05:50	answer . 28,248 . Okay , let's round out this
05:55	list with the last multiplication trickier . I don't use
05:57	this next one so much , but it still is
05:59	a pretty cool trick . Okay , so this is
06:01	the way this one works . Say for instance ,
06:03	I wanted to multiply 46 x 44 . This trick
06:08	is pretty specific and that's why I don't use this
06:10	one so much . You have to have a couple
06:12	of things that you fulfill the tens numbers have to
06:15	be the same . So in this case they're both
06:17	40 numbers , the units numbers have to add up
06:20	to 10 . Like I said , fairly specific ,
06:22	but pretty cool . Right ? So anyway , this
06:25	is the way this one works To get the first
06:27	part of her answer . We're going to get this
06:29	40 part and we're going to multiply it by the
06:31	next number after four , which is a 54 times
06:35	five is equal to 20 To get the second part
06:38	of our answer . We're just gonna multiply the two
06:40	units passed together . Six times four is equal to
06:43	24 , times 44 is equal to 2024 . What
06:49	about we give that a go one more time .
06:50	What about we go , 83 multiplied by 87 .
06:55	Okay . As you can see the tens , numbers
06:57	are the same . They're both eight . So the
06:59	first part is gonna be nine times eight , 9
07:02	, 8 , a 72 . For our last part
07:05	, the numbers add up to 10 , 7 times
07:08	three is equal to 21 and that's our answer .
07:11	7,221 . Anyway , another video , I'm going to
07:16	also show you a whole bunch of tricks to do
07:18	with squaring as well and some different ones to do
07:21	with percentages and things like that . So we can
07:22	group them all together anyway , tell us what you
07:25	thought of that video in the comments . And if
07:26	you like to give us a big thumbs up and
07:28	you've got to be a real powertech math , you
07:30	can always become a Patreon . You know , thank
07:33	you for watching . And we'll see you next time
07:34	. Bye .

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