@Sandeep: I think you are biased toward the favourable scenario where you've just seen X (say 5) black cards in a row and are thinking you should yell 'now'. You are dicounting the equallly probable scenario where you start by seeing X red cards in a row which is equally likely. For every favourable scenario there is an equally unfavourable one to counter-balance the average. So when you start playing, you might as well take your 50-50 chances and yell 'now'.