text: explain how i got this answer? 2 cards are selected at random from 10 cards numbered from 1 to 10. find the probability p, that the sum is odd,   i)if 2 cards are drawn together   the answer given is 25/45  how is that possible, can somebody explain me number of combinations of 2 cards  = 10c2 = 10!/(2!*8!) = 45  for odd combo we have 1 with 2,4,6,8,10 2 with 3,5,7,9 3 with 4,6,8,10 4 with 5,7,9 5 with 6,8,10 6 with 7,9 7 with 8,10 8 with 9 9 with 10  the total number of pairs is 25  therefore, probability is 25/45