Like others, I think that the answer is (D)
5^(k-1) > 3,000
<=> 5*5^(k-1) > 5*3*1000
<=> 5^k > 15 * 1000 > 1000
Cicerone, we do not care about k an integer or not. Actually, the function f(x) = a^x is definied for all x (removing a=0 to avoid a long dicussion done a while ago with Ps_dahaya
). A great exemple of it is a = e. f(x) = e^x.
So a question remains : where does this question come from?