> So you are averaging amounts of money, so you are averaging things that can be added and you are not averaging interest rates. So you're not doing what you th

> So you are averaging amounts of money, so you are averaging things that can be added and you are not averaging interest rates. So you're not doing what you think you were doing and everything is good. (1.2+1.5)/2 doesn't have a meaning but (1.2moneyA+1.5moneyB)/2=moneyAB and growth rate has nothing to do here You're taking a weighted average of interest rates. You can call it an amount of money if you like, but you can also call it a weighted average of interest rates. This is no different from a weighted average of time-varying interest rates over irregular intervals of time.