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Jack and Jill went up the hill to fetch a pail of water. But what happened when they got up there? They’ve been gone an awfully long time…
LCM & GCF 23649 Views
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Description:
OMG you should totes watch this vid. LOL. It’s all about LCM and GCF… FTW. Least Common Multiple and Greatest Common Factor, here we come. TTYL.
Transcript
- 00:04
LCM & GCF, a la Shmoop. Just what are these mysterious acronyms?
- 00:16
Top-secret government organizations? A new form of textspeak?
- 00:29
Or perhaps some misplaced Scrabble tiles? Actually, they are abbreviations of mathematical
- 00:33
concepts. We know -- you were hoping for the secret
- 00:43
organization thing. LCM is an acronym for Least Common Multiple.
Full Transcript
- 00:51
Let's take a look at that one first. Ooh, not so close. Let's back it up a bit,
- 00:58
boys. There we go. First we need to talk about what
- 01:02
a multiple is.
- 01:05
Say you've got the number 6. A multiple is any number that can result from
- 01:10
multiplying our given number by any other number.
- 01:14
For example, you can multiply 6 by 1 to get 6...
- 01:16
...by 2 to get 12...
- 01:17
...by 3 to get 18...
- 01:19
...by 4 to get 24, and so on.
- 01:21
6, 12, 18 and 24 are all multiples of 6.
- 01:26
If you want to find the multiples of 8, you can multiply 8 by 1 to get 8...
- 01:30
...by 2 to get 16...
- 01:31
...and by 3 to get 24. We could keep going, but we can see you're
- 01:35
in a hurry. If you want to find the Least Common Multiple
- 01:41
of 6 and 8, you need to find the smallest number that shares both numbers as factors.
- 01:47
As you can see, it's unfortunately not as easy as merely multiplying the numbers together.
- 01:55
GCF, or Greatest Common Factor, is basically the reverse.
- 02:04
When looking for a GCF, you need to find the largest number that will divide evenly into
- 02:09
two other numbers. Take the numbers 36 and 48.
- 02:14
Okay, wiseguy. Put them back. Suppose you are given the numbers 36 and 48.
- 02:19
What factors do they have in common?
- 02:21
Well, both numbers are even, so 2 works. 3 is also a factor, as are 4 and 6. But the
- 02:28
greatest common factor -- the granddaddy of them all -- is 12.
- 02:34
A good way to find the GCF - rather than by using trial and error - is to first use prime
- 02:40
factorization. 36 breaks down into 2 times 2 times 3 times
- 02:46
3. 48 breaks down into 2 times 2 times 2 times
- 02:51
2 times 3. The numbers that the two have in common are
- 02:54
two 2's and a three. Multiply those out and voila -- 12.
- 03:06
Practice finding LCM's and GCF's on your own, and it will pay dividends.
- 03:14
Just don't let the SITF catch you. Those guys are not to be trifled with.
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