Let S denote the success (getting a '6') and F denotes the failure (not getting a '6')
Thus P(S) = 1/6, P(F) = 5/6
P(A wins in the first throw) = p(S) = 1/6,
A gets the third throw, when the first throw by A and second throw by B result into failures. Therefore, P(A wins in the 3rd throw)
Decision : Referee's decision was fair because team spirit enhances co-operation and unity