Unformatted text preview: For the number 7, you just need to use your calculator on that one. But for 3 & 9, I have a different approach. First, if a 9 can go into a larger number you know that a 3 can since a 9 is a multiple of 3. But to see if 3 can go into a number a clever little way was given to me from that book. Let's take an example. ..say the number 7, 017. On the surface it looks like there is nothing that would go into it evenly. ..WRONG!!!! Add the digits of the number, that is 7 + 0 + 1 + 7 and it totals 15. If this number is divisible by 3 then the entire number is! Cute trick....
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 Spring '10
 
 Prime number

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