Ferihere wrote:

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 DS 131.

5^k>1000?

S1:

5^k-1>3000 ---> 5^k>15000. So this is suff.

S2:

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

5^k=625

So suff.

Ans is D.

If OA is B. Then S1 is written incorrectly. It should be written as 5^k+1>3000.