Let a * b = ab/(a - b). What is the value of (1*2)*3? Express your answer as a common fraction.
(1 * 2) = (1 * 2) / ( 1 - 2) = -2
(1 * 2) * 3 = -2 * 3 = (-2 * 3) / ( -2 - 3) = -6 / -5 = 6 / 5
