If your n = 1, you'll be betting:
3 on the 100x return boat
6 on the 50x return boat
10 on the 30x return boat
15 on the 20x return boat
30 on the 10x return boat
Doing this it will get you a guaranteed 300 cocktails as a reward by spending 64 (3+6+10+15+30) pearls for the bets.
For higher n values, you'll get 600 for 128, 900 for 192, 1200 for 256 and so on.