Use a growth rate equation which takes into account the number of time intervals in your data. To perform this on a hand-held calculator take the following steps. Year 1 growth 120000 100000 - 1 20.
Geometric Mean 23413.
The numbers in the problem have to be added together and then divided. Year 1 growth 120000 100000 - 1 20. To calculate your future balance in the above example the formula would be. Year 3 growth 160000 135000 - 1 185.