# Find the LCM – FAST!

Here’s a short video on how to find the LCM. It uses a trick that I have not seen anywhere else, and the approach is quite fast.

The information in this video dovetails with the info in this post.

I hope that you find this video helpful.

## 2 Responses to “Find the LCM – FAST!”

1. Irving Lubliner says:

Hi Josh,

I like your “quick and easy” way of finding least common multiples, but I have one concern. Your video does not caution students that it only works when you have just two numbers. A student watching your video might try to find the LCM of 8, 12, and 20 by dividing their GCF, which is 4, into the 8, and then multiplying by 12, and then by 20. Of course, a slight adaptation of the trick would yield the proper LCM for three or more numbers, but it is not addressed in your video. I would also be more excited if you explained the “why” behind the “how.”

Best,

Irv

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2. Cancel says:

There are some nice activities here. Thanks.The attviicy about even numbers being the sum of two odd primes is called Goldbach’s conjecture, and is a famous unproved conjecture in mathematics. This is a really nice example that shows mathematics as a living subject, with problems for which we don’t yet have an answer. Researching some of the historical aspects of primes and Goldbach’s conjecture is a great cross-curriculum attviicy.Also, if Goldbach’s conjecture for even numbers happens to be true, the result about odd numbers greater than 7 being the sum of 3 odd primes follows logically. Why? This is a good exercise in logical reasoning for children.

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