The fast food company paid the hamburger bun company $120 per 100 hamburger buns. The fast food company charged their customers the same for 3 hamburger buns as they paid for 5. What was the profit the fast food company made per hundred hamburger buns?

For the fast food company:
Cost of 100 hamburger buns = $120
Hence, cost of 5 hamburger buns = (5*120)/100 = $6
For the customer:
Cost of 3 hamburger buns = $6
Hence, cost of 100 hamburger buns = (100*6)/3 = $200
The fast food company bought 100 buns for $120, and sold those 100 buns for $200.
Hence, the profit per 100 buns = 200 - 120 = $80