Three people agree to share a 90-unit expense equally. Each share is 30. If one person pays the provider in full, the bill has been paid, but the agreed reimbursements between the people remain.
Separate the two relationships
Record the provider’s total once, then record each person’s share and contribution. Do not add the later reimbursements to the original bill and conclude the activity cost 150. Those transfers settle the shared expense; they are not additional purchases in this example.
Confirm what belongs in the split
If one person adds a private 12-unit item, agree whether it is excluded before dividing. Under an equal split of the shared 90 plus that separate item, the shared shares remain 30, while the additional item belongs to its buyer.
Keep the exercise’s assumptions beside the arithmetic. Real arrangements may use different proportions or exclude other costs. A clear record of the agreed total, sharing rule and payments is more useful than a single unexplained number sent to the group afterward.