You may not have the same result...

You may not have the same result depending where the offer starts.

In [1]: list(zip(range(150, 1500, 50), range(1000, 100, -100))) Out[1]: [(150, 1000), (200, 900), (250, 800), (300, 700), (350, 600), (400, 500), (450, 400), # stops here since her offer > next old man's offer (500, 300), (550, 200)]

In [2]: list(zip(range(1000, 100, -100), range(150, 1500, 50))) Out[2]: [(1000, 150), (900, 200), (800, 250), (700, 300), (600, 350), (500, 400), # stops here since her offer == next old man's offer (400, 450), (300, 500), (200, 550)]

When you want to buy something, you generally ask for a price first. So the offer starts with the old man at 1000 and ends to 400.