well it depends on what deck they are dealt
a standard deck is 52 card, 26 black, 26 red
the chance of the first card being red = 26/52 (1/2)
second card, 25/51
3th card: 24/50
the chance of these 3 events happening just after eachother =
26/52 25/51 24/50 = 262524 / (525150) = 15 600 / 132 600
this fraction equals = 2/17th