| Here is a straight foward explanation; This is a simple permutation problem...
5 cards arranged in random order (no repetition):
5! = 5*4*3*2*1 = 120 total combinations
Subtract the number of combinations possible with C at the end.
That value = 4! because C is fixed and there are 4 cards left to be arranged in random order.
4*3*2*1 = 24
Multiply this by 2 to account for the other end,
24*2 = 48
120 total - 48 with C at the end
120 - 48 = 72 |