Powers of 2 are extremely important. If you're not really good with memorizing a lot of info on quant (IMHO you should know all the powers of 2 up to the tenth power), then I suggest you memorize at least 2^10 = 1024. IT specialists will obviously state that this is a pretty important thing to note.

So if you know that 2^10 = 1024, you will be able to tell in like 5 seconds that 2^9 = 1024/2 = 512. Consequently, 2^8 will obviously be smaller than 500, so it's off the list.

The minimum will be 9.

Thanks for the quick reply. I knew how to do it by memorizing and writing it out. Just wondering if there's a way to do it through algebra and equations.

No, I don't think there's any other way to do this. You could also use the approach of multiplying 2*2*2... until you hit 500, but this is laborious and will take a lot of time, time you don't have on the GMAT.

But take it from someone who knows all the squares up to 20, all the cubes up to 11 and essential powers of 2, 3 and 5: memorizing some powers will always be a good idea. I remember seeing some questions (bout 2 or 3, I believe) in the beginning of my exam that I solved in seconds using my "internal database". This helped me create a time reserve that I later used for harder questions.