For 2 independent systems at 60% win rate each, the probability of both being wrong is (0.4)*(0.4) = 0.16, so the win rate when both agree is 1 - 0.16 = 84%.
For 3 independent systems at 60% win rate each, the probability of all three being wrong is (0.4)*(0.4)*0.4 = 0.064, so the win rate...