Least Common Multiple (LCM)

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Being able to find the least common multiple of two numbers is very useful, as it will allow us to add and subtract fractions, and do all kinds of other cool things. One way is to list all the multiples and look at the lists, but this gets tricky as numbers get bigger, so learn a neat trick for how to do this quickly!
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Опубликовано:

21 авг 2017

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Комментарии : 87

@DylRicho 4 года назад

I prefer the terminology 'lowest common multiple' because "least common" can be misinterpreted as something entirely unrelated to the question at hand. With "lowest," you know that you're just looking for the smallest multiple that is found between all numbers in a given question.

@girirajvardhan2722 7 месяцев назад

Can you explain with context?

@Catimixto 2 месяца назад

It's even worse in spanish, "Mínimo común multiplo"

@travelvids9386 7 дней назад

@girirajvardhan2722 least common can also mean rare.

@etherealbladerx8153 3 года назад

You're "Checking Comprehension" music is as if the one who composed Earthbound music tried his hand at making the Wii shop channel music 😂 just a little funny to me 😊 great stuff as always

@vdvoskin1 11 месяцев назад

there is an easier way to find the lest common multiple. lets take 18 and 24. start dividing both members by any common number that will yield a whole number, so first division is by 2: 18/2=9 and 24/2=12, remaining numbers can be further divided so we continue, second division is by 3: 9/3=3 12/3=4, we cannot divide anymore so we simply multiply the remaining numbers by the numbers we used to divide: 3*4*2*3=72.

@sandpaper6095 11 месяцев назад

Genius

@vaibhavgore165 7 месяцев назад

🙌

@rizzwan-42069 5 месяцев назад

lemme try 12 and 80 divide by 4: 3 and 20. 20×3×4=12×20 clearly 240 this works and it's faster.

@maithrisiri 4 месяца назад

Thanks

@davemaciver3681 3 месяца назад

I'm planning to go back to uni in the next couple of years to study nursing which needs higher maths for some reason and I zoned out by that stage as I was already going to college for acting. I was GREAT at maths when I was in school, went to master classes and everything, but haven't bothered with it for 2 and a half decades. We're getting to the point of the course where I'm feeling proud of myself for getting stuff right! Thanks other Dave :)

@emcmnd4196 3 года назад

I figured out a incredibly fast way to find the least common multiple of two numbers. That is to find the ratio between the numbers and then simlify it into the simplest fraction form. Finally, multiple the small number of the two number with the big number of the fraction or the oppsite. The result is the least common multiple of the two numbers

@NickHope 2 года назад

By that method you can either multiply the numerator (the top number) of the simplified fraction by the denominator (the bottom number) of the original fraction, or vice versa with the same result.

@albabahmed2735 3 года назад

You are a blessing to us who forgot how to do basic math :D

@suzi8364 3 года назад

Me :3

@user-ri7qy1en7l 3 года назад

@@suzi8364 I forgot the multiplication table and now here I am starting from the very first

@jayw8726 4 года назад

I took me 20years to properly understand this since this was first explained in Grade 4 back in year 2000! Reckon my teacher was really lacking in her pedagogy! 😂

@aliaoda8864 2 года назад

Same

@ignacioleikis1784 4 года назад

So the way to calculate the LCM of two numbers is to take the greatest number of factors of one number with the greatest number of factors from the other, irregardless of whether one factor repeats from one number to the other?

@aashsyed1277 3 года назад

yep. it's not told in other countries but it is told in india& pakistan

@anthonystark6215 Год назад

Thank you, Professor!

@lisaleidy344 Год назад

So helpful, thank you.

@AbhishekDwivedi-zx5nv Год назад

Thank you Professor .

@torosalvajebcn 5 лет назад

Another way to know which fraction is bigger is by cross multiplication

@IzeDesu 5 месяцев назад

yes its easier but in some equations its more relevant to use LCM

@4karma860 Год назад

10% done with the playlist :3

@Carrymejane 7 месяцев назад

HAHAHAHAHAHSAHAW

@SteveJobs-qd7mk Месяц назад

16.5

@user-xf6zw5jy5v 3 года назад

This helped allot

@MiltosPol-qn3zh 7 лет назад

Very good

@yeayeah8321 3 года назад

Thank you

@user-sd7zf9fi7s 6 месяцев назад

you have taught me more math than anyone, thank you Dave

@sultanmo9631 2 года назад

Not me, a senior engineering student learning about LCM here :)

@timurnachname1681 7 лет назад

What do you Think about the euclid Algorithm for LCM and HCF?

@surjeetkumarsingh8251 6 лет назад

Timur nachname 2

@ljr6490 Год назад

Isn't this kinda similar to an OR operator with the joining the most abundant primes?

@Zone_Ranger 7 лет назад

I like to use LCM(a,b)=a*b/GCD(a,b)

@mayankarora5377 Год назад

what if the GCD of both numbers is 1 ? then this formula will imply LCM^2 which is obviously incorrect

@Zone_Ranger Год назад

@@mayankarora5377 then the lcm(a,b)=a*b

@chourouk-gr9qg 25 дней назад

Thnx man

@tres-2buniverse729 6 месяцев назад

I think there is a simpler way to find the least common multiple by finding the biggest number which can divide both of the members,6 in this case 18/6=3 24/6=4 since 6 is common multiple for both numbers, then we multiply it with the result of the smallest numbers 3.4.6=72 (I dont know what Im doing though I suck at math so dont take this comment seriously)

@tres-2buniverse729 6 месяцев назад

20/4=5 28/4=7 5.7.4=140 it worked for the second one too I think this works

@tres-2buniverse729 6 месяцев назад

14/2=7 36/2=18 18.7.2=252 still works

@tres-2buniverse729 6 месяцев назад

50/5=10 65/5=13 13.10.5=650 and this is the last still works too,I find it easier to multiply relatively bigger numbers compared to simplifying a big number

@Warlocktopus 7 лет назад

i thought LCM stood for lowest common multiple. I learned something ^^

@ProfessorDaveExplains 7 лет назад

lowest = least, same thing!

@topiado2073 3 года назад

@@ProfessorDaveExplains 😄

@sing3210 6 месяцев назад

Also this is soo helpful ❤

@user-vh4jn4vv8e 6 лет назад

Nice

@yatu9002 Год назад

4:17 wait how is 4/12 bigger than 3/12 because when you divide you get 3 > 4 how it should be 4 > 3 or it is about how many times does the number fit into if the number fit's into it

@shubhampal5328 Год назад

Dividing 4 into 12 parts will always be greater than diving 3 into 12 parts.

@lutherjeremy6150 Год назад

hello, let me help yatu, imagine it's a circle piece of 4/12 and 3/12, if you simplify the 4/12 and 3/12, you get 1/3 and 1/4. Well, 1/3 circle is bigger than 1/4 circle right ? hope it helps🙏🏾

@sphephilezwane5539 Год назад

You the best😭😭❤️❤️

@jonnyabatti5120 3 года назад

In the comprehension 18 24, i factored 24 -> 12*2 and then 12 -> 4*3 and then 4 -> 2*2. Why am I wrong? Hope you can help me

@asifbaig3811 3 года назад

in order to find LCM we have to divide by lowest number because we have the lowest number 24/12= 2 and 18/9 = 2 so we won't be able to find least number. To find you have to 2 (24,18) 2(12,9) 2(6,3) 2(2,3) 3(1,3) (1,1) 2*2*2*2*3

@asifbaig3811 3 года назад

Please ignore the explanation is wring

@zemo7483 2 года назад

You have to write only primes as it factors. They are 24= 2*2*2*3 18=2*3*3 Now the 2 appears three times in 24's factors and, 3 appears twice in 18's factors so , LCM= 2*2*2*3*3 = 72

@Lewis_8 Год назад

@@zemo7483 72 you mean...

@zemo7483 Год назад

@@Lewis_8 yes

@tulsidevi6768 4 года назад

Why unlikes for this video,🤔🤷

@riiachka 4 года назад

prof dave, i think that in the checking comprehendsion the answer for 18 and 20 is wrong. shouldnt it be 180?

@ProfessorDaveExplains 4 года назад

that's not one of the questions

@riiachka 4 года назад

@@ProfessorDaveExplains oh sorry i meant 24, not 20

@jonnyabatti5120 3 года назад

Joey Koch what i dont get is 24 if i factor it 12*2 and go from there i get the wrong answer. So when doing this what do i havw to keep in mind

@jonnyabatti5120 3 года назад

In the comprehension 18 24, i factored 24 -> 12*2 and then 12 -> 4*3 and then 4 -> 2*2. Why am I wrong?

@0Coeus 3 года назад

@@jonnyabatti5120 Nothing in your comment is wrong, you are just not done with all the steps. The prime factorisation of 24 is 2*2*2*3 (this is what you did) The prime factorisation of 18 is 2*3*3 To find the least common multiple you take the multiples of each whole number from the factorisation that has the most. 24 has three of the number 2, while 18 only has one, so we take the three. 18 has two of the 3's, while 24 only has one, so we take the two: 2*2*2*3*3 = 72 The video does not explain why this works, so I guess thats a story for another time :)

@sanjayx5394 Год назад

Lcm

@sing3210 6 месяцев назад

Haha I love ur theme song

@TaeKinzel Год назад

I heard one fast food place made a 1/3 burger but people thought it was smaller so it didn't work out.

@salah1x 3 года назад

I understand it pretty well now, but I still don't find any useful application for it. I can find which fraction is greater simply by converting it to decimals instead of doing all of this

@alexionut.05 3 года назад

works for small fractions. but it is highly unlikely that you are going to convert something like 57/960 into decimal. easier to find the lcm between 960 and whatever other number you are comparing it to.

@OwlbaTr0ss 3 месяца назад

why does this work tho? I understad the process but I do not understand why it works, is it just one of those stupid "that's just the way it is in math things that just works and we don't know why"?