Answer of the puzzle (Average Salary) is :
Lets assume their names are A, B and C and their salaries are 100, 200 and 300 in the same order. If you wish you can replace with some variable like X, Y or Z
Now A will not tell his salary directly to B but add some random value (lets say 50) so the salary he would tell to B would be 150 (his salary plus some random value). Remember A will only tell to B, which C cannot hear.
Now B will add his salary plus some random value (lets say 60) and add with the salary he got from A. This would become 410 (150+200+60). Now B will tell this amount to C, which again A cannot hear.
Similarly C will add add his salary plus some random value (lets say 70) to the salary he has got from B. This would become 780 (410+300+70). C will tell this amount to A, which B cannot hear.
Now A will subtract his dummy amount (50) from this amount and tell B. B will get 730
Similarly B will subtract his dummy amount (60) and tell C. C will get 670
Finally C will subtract his dummy number (70) and tell A. A will get 600.
Now 600 is the sum of their salary so the average would be 200 (600/3)
