You should read the problem a lot more carefully.
Can you explain how you got that answer? I don't believe so.
This is very similar to some of the other problems you have asked; try to make a connection so you know how to solve similar problems.
You have asked this question before and I have answered it.
Hint: Use constructive counting.
If you really want to be ahead of the curve, take advantage of AoPS classes. I'm recommending them for their level of depth.
I believe you are right. And summation is an amazing tool as well. You should expose yourself to it.
Whoa, no need to get belligerent like that. I was just pointing out that I don't really consider that solution elegant, and that's my opinion. I think that it's possible to do it faster if you know the formula for the sum of a geometric series.
Totally unrelated, but answering questions here is fun and I should do it more.
When you ask a question, could you tell us what is confusing you so we can better help you?
