Multi-Spreadsheet · Multi-User · Enterprise-Scale Thought Experiment
By Hiran de Silva
Background
This challenge is inspired by a request from Ellen, who asked whether there were any more multi-spreadsheet, real-world Excel challenges available.
In response, this challenge has been created today, and it will also serve as a demo case for an upcoming Mission Possible – Episode One.
Scenario
Six friends from New York City are planning a trip to London:
- Chandler
- Monica
- Ross
- Rachel
- Joey
- Phoebe
Each of them books expenses in advance on behalf of the group.
These expenses include (but are not limited to):
- Hotels
- Travel
- Entertainment
- Restaurants
- Other shared activities
Each expense is paid by one person, and the cost is then shared equally among a defined subset of the group.
What You’ve Been Given
Inside the supplied ZIP file, you will find:
- 40 individual expense submissions
- Each submission records:
- Who paid
- What the item was
- The booking date
- The total amount
- The list of people who agreed to share the cost
Each expense belongs to one of the six friends.
Level 1 – Immediate Requirement (Trip to London)
After processing the 40 expense submissions, the system must be able to answer:
- How much is owed
- By whom
- To whom
In other words:
Produce a clear reconciliation of balances between the six friends.
They must be able to see clearly what they are owed, or owe, at any time.
Level 2 – Ongoing, Unattended Operation
This is not a one-off exercise.
The London trip is just the beginning.
The system must be designed to:
- Handle ongoing expense submissions
- Reconcile balances continuously
- Operate unattended
- Require no single administrator
- Automatically update who owes what as new expenses are submitted
Level 3 – Scalability (Central Perk Expansion)
Downstairs from the apartment is Central Perk, a busy café.
- Gunther works behind the bar
- Many customers use Central Perk as their social hub
There is a real possibility that this system may need to expand beyond the six friends to:
- Hundreds
- Potentially thousands of users
The system must therefore be:
- Scalable
- Multi-user
- Capable of handling large numbers of participants without redesign
Technology Constraints
- Each participant:
- Has their own computer
- Uses Excel
- May be anywhere in the world
- Participants are:
- Not sharing a computer
- Not necessarily in the same building
- Not necessarily online at the same time
What’s Required of the Participant
You may respond in either of the following ways:
- Create the solution
Build a working system that meets the requirements. - Design the solution
Clearly outline:- The architecture
- The data flow
- How it scales
- How it runs unattended
Why This Challenge Exists
This challenge is designed to test:
- Multi-spreadsheet thinking
- Multi-user architecture
- Real-world reconciliation logic
- Scalability beyond “single-workbook Excel”
- Systems thinking rather than formula tricks
It is deliberately framed as a real enterprise-style problem, disguised as a friendly, familiar scenario.
Summary
Level 1:
Reconcile balances between six friends after 40 expenses.
Level 2:
Make the process ongoing and unattended.
Level 3:
Design for scale — potentially hundreds or thousands of users.
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