Suppose I take a taxi with a friend. She gets out when the fare is $3 and I get out when the fare is at $6. How should we distribute the total cost fairly?
One idea is that I should pay double what my friend pays. $6 = X + 2X where X is the amount paid by my friend. So I would pay $4. But another idea is that we should share the fare up to her exit, then I should pay alone after. So X = $3/2 where X is the amount paid by my friend.