Talk to Banion in the Gambler's Hideout on the 10th Floor in the Abandoned Apartment in Gohtza. He'll ask you for a loan and asures you that he can win your money back. Loan him 1,000g. And he will give you Loan Papers. Leave the zone and talk to him again. You will have the option to give him another loan or get your money back. Don't ask for your money back. Instead agree to give him another 1,000g. Then leave the Casino and come back and repeat. You will do this a total of 10 times (you will need to give him 10,000g) . Talk to him the 11th time and he will give you 50,000g. (that's a pretty good investment).
You get to invest in him a total of 10 times. Every gold you invest pays back five gold, so if you invest 100g x 5, 500g x 4, and 1000g (3500g) he will pay you back 17500g.
- 40,000g Profit.