Here is a little mathematical exercise for you. At 7% per week, how long does it take for one bitcoin to collect a compound interest of 10 million bitcoins? The first to answer this question correctly gets BTC0.1 from me (raising the question how long it would take for that tiny amount). 
It takes 205 weeks, or slightly less than 4 years:
>>> math.log(1e6, 1.07)
204.19430286596887
>>> float(205) / 52
3.9423076923076925