Khan Academy on a Stick
Factors and multiples
Understanding and finding factors and multiples. After these videos, you'll be ready for fractions.

Divisibility Tests for 2, 3, 4, 5, 6, 9, 10
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Worked example of basic divisibility tests

Recognizing Divisibility
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Recognizing Divisibility

The Why of the 3 Divisibility Rule
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Why you can add the digits to see if something is divisible by 3

The Why of the 9 Divisibility Rule
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Why you can test divisibility by 9 by just adding the digits
Divisibility tests
Whether you are trying to impress your dog's friends (who are obsessed with figuring out number divisibility) or quickly factor a number, it can be very useful to tell whether a number is divisible by another. This tutorial walks through some of the more standard divisibility methods and describes why they work.

Finding Factors of a Number
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Finding Factors of a Number
Divisibility and factors
In this tutorial, we'll begin to think about the numbers that "make up" the number. This will be useful throughout our study of math. Whether we are adding fractions, exploring mystical number patterns, or breaking computer codes, factoring numbers are key! Eye of the tiger!

Prime Numbers
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Identifying prime numbers

Recognizing Prime Numbers
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Recognizing Prime Numbers
Prime numbers
Prime numbers have been studied by mathematicians and mystics for ages (seriously). They are both basic and mysterious. The more you explore them, the more you will realize that the universe is a fascinating place. This tutorial will introduce you to the magical world of prime numbers.

Prime Factorization
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Prime Factorization

Common Divisibility Examples
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Common Divisibility Examples
Prime factorization
You know what prime numbers are and how to identify them. In this tutorial, we'll see that *all* positive whole numbers can be broken down into products of prime numbers (In some way, prime numbers are the "atoms" of the number world that can be multiplied to create any other number). Besides being a fascinating idea, it is also extremely useful. Prime factorization can be used to decrypt encrypted information!
 Least common multiple exercise
 Least common multiple exercise 2

Least Common Multiple (LCM)
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Least Common Multiple (LCM)

Old Least Common Multiple
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Example of figuring out the least common multiple of two numbers. This is one of the very first videos made on Khan Academy. Mistake notice: Sal forgets 56 as a multiple of 8.
Least common multiple
Life is good, but it can always get better. Just imagine being able to find the smallest number that is a multiple of two other numbers! Other than making your life more fulfilling, it will allow you to do incredible things like adding fractions.

Greatest Common Divisor
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4 example problems of determining the greatest common factor of two numbers by factoring the 2 numbers first
 LCM and GCF (greatest common factor) word problems
Greatest common divisor
You know how to find factors of a number. But what about factors that are common to two numbers? Even better, imagine the largest factors that are common to two numbers. I know. Too exciting!