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h_div_rules

# h_div_rules - DIVISIBILITY RULES AND PRIME FACTORIZATION...

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VC DEPARTMENT OF MATHEMATICS REVISED FALL 2005 DIVISIBILITY RULES AND PRIME FACTORIZATION 2 (Prime) A number is divisible by 2 if its last digit is 0, 2, 4, 6, or 8. Any even number is divisible by 2. 3 (Prime) Add all of the digits composing the number. If the sum of the digits is divisible by 3, then so is the original number. Example : If the number is 564, add 5 + 6 + 4 = 15 . The sum of the digits (15 ) is divisible by 3, so 564 is also divisible by 3. 4 (Composite) A number is divisible by 4 if the number formed by its last two digits is divisible by 4, or if the number ends in 00. Examples : The number 5748 is divisible by 4 because the number formed by its last two digits (48 ) is divisible by 4. The number 300 is divisible by 4 because it ends in 00 . 5 (Prime) A number is divisible by 5 if its last digit is 0 or 5. 6 (Composite) A number is divisible by 6 if it is divisible by both 2 and 3 (see above). 7 (Prime) Draw a vertical line between the tens’ and ones’ digits, so that there are now two “numbers.” Multiply the rightmost “number” by 5, and then add the leftmost “number” to the product. If
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