When a die is rolled three times. Then, cardinality of sample space =63 Now, according to question, the favourable outcomes =(1,2,3),(1,2,4),(1,2,5),(1,2,6),(1,3,4),(1,3,5), (1,3,6),(1,4,5),(1,4,6),(1,5,6),(2,3,4), (2,3,5),(2,3,6),(2,4,5),(2,4,6),(3,4,5), (3,4,6),(4,5,6),(2,5,6),(3,5,6) ∴ Required probability =