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A friend and I are completely stumped on this prompt, and are even having trouble seeing how its statement is true. Any help will be appreciated!

Prove that if $a \equiv b \pmod{3}$, then $2a \equiv 2b \pmod{3}$.

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    Hint: $a = 3n + b$2012-10-24
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    If $a-b$ is divisible by 3, then $2a-2b=2\cdot(a-b)$ ... ?2012-10-24

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