Suppose that we are $6$ guests for renting a house, $2$ are going to spend three nights in the house while $4$ of them are going to spend just $2$ nights in this house. The problem is that if the bill of renting this house is $x$, how can we share it? Two possible solutions are proposed:
- The total of nights for the group is $$3+3+2+2+2+2=14,$$ so the people who are going to stay in the house $3$ nights have to pay $3x/14$, the rest $2x/14$.
- One night is totally paid for the $2$ guests $x/3$ and they also have to pay the proportionally part of the two following nights $(2x/3)/6$. The rest only have to pay these last nights $(2x/3)/6$.
The thing is that for an arbitrary $x$ the payments are different for the people. In the first case is not fair for the $2$ nights guests because they are sharing the total amount, but this is the most reasonable solution because they pay exactly $2/3$ less than the $3$ nights guests. However, the $3$ nights guests have to pay considerably more amount in the second case (2.5 times more) than the $2$ nights guests. Which one is the correct answer?
Neither answer is more correct than the other - they are just different ways of dividing up the total rent, which give different results.
In the first approach every one pays the same amount per night, but the 4 guests who are only there for 2 nights may feel they are subsidising the 2 guests who are there for 3 nights because they are paying more than (2X/3)/6 = X/9 each.
In the second approach the 4 guests who are there for 2 nights pay X/9 each and the other two guests pay 5X/18 each - but the other two guests may feel this is unfair because they are now paying on average more per night than the other guests.
You could go with either approach but probably best to reach agreement beforehand to avoid arguments.