Answer: Tuesday Teaser #7
There are several answers to this problem. My favourite way is for the first person to add a random number to his salary and then tell the sum to the second person. The second person would then add his salary to the sum and tell the third person. Each person would then continue in this way until the last person adds on his salary and tells the first person. The first person can now subtract his random number and divide the total by the number of people to find the average.
Interestingly (perhaps), using this method the last person is able to work out the random number that the first person added and so he and the second person could easily work out the salary of the first. Given this, if we’re worried about revealing any of the individual salaries, it actually seems safer for each person to put their salaries in a hat and for the average to be calculated that way.
