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How did they know 3^(4n-2) / 10 always ends in a 9?

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Source: — Data Sufficiency |
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by palvarez » Mon Nov 16, 2009 1:24 am
look at the series of 4n-2.

2, 6,8, ....

3^2 = 9,
3^6 = 9
and so on, note that 3^4 = 81.
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