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Is it true that if $3|x$ and $3|y$ and $3|z$ then $3|(x+y+z)?$
If yes how do I prove it?
If not how do I work through a problem like this?

user376343
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Johhny Smith
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  • What does TD mean? – coffeemath Jan 30 '20 at 06:04
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    @coffeemath Test for Divisibility maybe? – almagest Jan 30 '20 at 06:19
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    @JohhnySmith Beware of abbreviations like TD unless you are really sure they are in general use. I have been in math for decades and have no idea what it means. The fact that a book uses it is far from conclusive evidence that it is widely used. – almagest Jan 30 '20 at 06:21

1 Answers1

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$3a=x,\ 3b=y,\ 3c=z,$ now factor out $3$ and put $d=a+b+c.$ Then $3d=x+y+z$ so...

coffeemath
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