Number of ways in which one of the face having the number 6 and no two dice show the same number.
(1,2,6),(1,3,6),(1,4,6),(1,5,6),(2,3,6),(2,4,6),(2,5,6),(3,4,6),(3,5,6).....
Total favourable case
=20+20+20=60.
Number of total output when three top faces of three dice shows different number
=6×5×4=120.
∴ Required probability
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