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Example:FindMissing Digit using Divisibility Test

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Explanation:

Divisibility rule

A divisibility rule is a shorthand way of discovering whether a given number is divisible by a fixed divisor without performing the division, usually by examining its digits.

### Divisibility by 3

First, take any number (for this example it will be 492) and add together each digit in the number (4 + 9 + 2 = 15). Then take that sum (15) and determine if it is divisible by 3. If the final number is divisible by 3, then the original number is divisible by 3. (Our solved example in mathguru.com uses this concept)

If a number is a multiplication of 3 consecutive numbers then that number is always divisible by 3. This is useful for when the number takes the form of (n × (n − 1) × (n + 1))

Example:

1.  492 (The original number)

2.  4 + 9 + 2 = 15 (Add each individual digit together)

3.  15 is divisible by 3 at which point we can stop. Alternatively we can continue using the same method if the number is still too large:

4.  1 + 5 = 6 (Add each individual digit together)

5.  6 ÷ 3 = 2 (Check to see if the number received is divisible by 3)

6.  492 ÷ 3 = 164 (If the number obtained by using the rule is divisible by 3, then the whole number is divisible by 3)

http://en.wikipedia.org/wiki/Divisibility_rule

The above explanation is copied from Wikipedia, the free encyclopedia and is remixed as allowed under the Creative Commons Attribution- ShareAlike 3.0 Unported License.

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