If I have 0$ at the moment can I make 100$ in 2 or 3 months? How?
What if I deposited 20$ .. Can I make them 100$ in less time?
You can actually earn more than that specially if you are skilled and fully determined enough. Through joining such sigmature campign, bounty program, and other service which is offered in this forum, you can earn more than $100 in less than or more than a month. If your target is 2-3 months, it's quite tangible without any investments.
But to build an activity to full member it takes 4 months and not necessarily in full member earn us can get $100 and received in signature campaign, I agree with you and It's true that as long you have enough skill you can earning how much that's.