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Exponential question

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Source: — Data Sufficiency |
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(2) is alone sufficient, but (1) is not.

by praxis » Mon Mar 02, 2009 7:10 pm
(1) is not sufficient because
5^(k+1) > 3000
is equivalent to
5^k > 600

Which is not sufficient

(2) is sufficient because
5^(k-1) = 5^k - 500
is equivalent to
(1/5) * 5^k = 5^k - 500 and collecting terms we get
500 = (4/5) * 5^k
5^k = 2500/4, which is less than 1000.

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