gistfile1.txt

irb(main):028:0> x = 10_000
=> 10000
irb(main):029:0> 20.times { x = f(x, 0.07); puts x }
10700.0
11449.0
12250.43
13107.9601
14025.517307
15007.30351849
16057.8147647843
17181.8617983192
18384.592124201547
19671.513572895656
21048.51952299835
22521.915889608237
24098.450001880814
25785.34150201247
27590.315407153343
29521.63748565408
31588.152109649865
33799.32275732535
36165.275350338125
38696.84462486179
=> 20