It is easy but I don't agree with OA
What is the source of this problem? B/c this looks astonishingly similar to OG11
5^k-1>3000 ---> 5^k>15000. So this is suff.
5^k/5=5^k-500 (multiply the 5) ---> 5^k=5^k+1-2500. Here I just tried values.
k=4. Is the only one that works.
There is an alternative if u don't want to plug and chug.
5^k-5^k-1=500. 5^k-5^k(1/5) ---> 5^k(1-1/5) ---> 5^k(4/5) =500
Ans is D.
If OA is B. Then S1 is written incorrectly. It should be written as 5^k+1>3000.