My bad maths...

I play Whist at work, but am struggling with a very basic maths prob!!! I've tried google, but can't find anything and my head is spinning.

General idea on the last round of the game:
each player gets dealt 1 card, then the top of the pack is turned up as the Trump, then each player "bids" in turn. But the bids can't add up to the cards dealt (1). Eg: player A bids 1, player B bids 0, player C has to bid 1.

On this particular game, there were 3 players.
Player A gets dealt the 4h.The trump is 10d (so diamonds).

So should player A bid 1 with 2 players behind him?

Cards that beat him: 12d's, 10h's = 22 cards
Cards that can't beat him : 13c's, 13s's, 3h's = 29 cards.

The answer is probably yes on this occasion, but how does the probablity change as the players increase? Anyone give me the formula???