Interview Question for Financial Software Developer at Bloomberg L.P.:

Weight 6 random buttons. (3 + 3)
    If weight is equal - you need to weight last 2.
    else - select 3 which was heavier and weight 2 random from them.
                if 2 are equal - your heavier is 3-rd
                else - you found it.

Simple binary search. Let's say 3's your number

1 2 3 4 | 5 6 7 8 -> Left side is heavier
1 2 | 3 4 -> Right side is heavier
3 | 4 -> 3 is heavier than 4