text: Number of combinations of 2 cards  = 10C2 = 10!/(2!*8!) = 45\n\nFor odd combo we have\n1 with 2,4,6,8,10\n2 with 3,5,7,9\n3 with 4,6,8,10\n4 with 5,7,9\n5 with 6,8,10\n6 with 7,9\n7 with 8,10\n8 with 9\n9 with 10\n\nthe total number of pairs is 25\n\ntherefore, Probability is 25/45