Low Risk Investment with 20% Annual Return

Buy positive cash flow rent property using the leverage. Here's the assumption:

Price P, downpay 20%*P = 0.2P
Hold for 10 years, the value of the poroperty 2P (apply an assumption (or statistical facts?) that in average the house price doubles every 10 years)

The annual return rate r, 2P-0.8P = 0.2P(1+r)^10
so r = 6^0.1 - 1 = 19.6%

Here we simplified the assumption by not considering the principle decrease, and rent increase. Assume rent can cover all PITI, maintanence, management cost.

For comparison, if you using your own money without leverage:
your investment annual return would be r = 2^0.1 - 1 = 7.18%
(2P = P(1+r)^10)

So, the key for RE investment is cash flow & leverage!