Average Monthly Salary

During a school lunch break, ten kids are discussing about their holiday jobs. In particular, they would like to know their average monthly salary (for the ten of them), but no one wants to admit openly exactly how much they make. Can you devise a way for them to calculate their average (mean) salary without anyone having to tell anyone else what their individual salaries are?


There may many possible solutions, here is a simple one:

The first person takes his monthly salary (lets say $100), adds an arbitrary amount that only he knows (lets say $475) and whispers that number ($575) to the second person. The second person then adds his monthly salary (lets say $150) to that value and whispers the new total ($725) to the third person. The third person adds in his salary, whispers the new total to the fourth person and so on until the tenth person adds in his salary and whispers the final total to the first person. The first person then subtracts his arbitrary number from that total, divides by 10, which produces the average monthly salary for the group without anyone having to divulge their salary to anyone else.

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