Return on investment is the amount of profit on the invested money after deducting taxes, safety of investment is the risk factor involved in the investment. Such as risk is high safety of investment is less.
There is no norm. The internal rate of return should exceed the cost of capital. A low risk, on going enterprise might be satisfied with an IRR = 7- 10%, while a more risky venture might require 15-...
Calculating the return on investment you actually want to know whether the investment will give you positive value in the end. You wouldn't want to waste your money, right? Thus you want to make sure...