24 December 2017
Short puzzle relevant to some diversity and inclusion threads that encourage people to share salary info. (I should tag this as "citation needed" because I don't remember where I heard it.)
Alice, Bob, Carlos, and Dave all want to know the average salary of the four, but none wants to reveal their individual salary. How can the four of them work together to determine the average? Answer below.
Alice generates a random number, adds it to her salary, and gives the sum to Bob.
Bob adds his salary and gives the sum to Carlos.
Carlos adds his salary and gives the sum to Dave.
Dave adds his salary and gives the sum to Alice.
Alice subtracts her original random number, divides by the number of participants, and announces the average. No participant had to share their real salary, but everyone now knows if they are paid above or below the average for the group.