Source:Â www.firesides.ca

Many novices–especially those of us who were marginal math students in school–become intimidated by mention of percentages. AllowÂ me to simplify this discussion by emphasizingÂ only those common “must know” percentagesÂ and WHY YOU NEED TO KNOW THEM.

First, what odds does one require to bid a “good” slam or game? A game requires a 40%Â chance if NOT vulnerable, a 38% chance if vulnerable.Â This is calculated by factoring in the riskÂ (-50 or -100) of down one versus the reward ofÂ making (+400 or +600) the game. Apparently, theÂ people who calculate these odds have never beenÂ doubled and have never been down more than one. ðŸ˜†

A SMALL slam requires a 50% chance. VenturingÂ into a small slam which requires AT MOST a (50-50)Â finesse is considered GOOD bidding. Assaying aÂ small slam which will depend on AT LEAST a finesseÂ is BAD bidding. I would add my own general ruleÂ to this popular concensus: bid 50% 6NT slams, butÂ AVOID 50% SUIT slams. The chance of a RUFF in theÂ suit slam may be incalculably small, but might tiltÂ the balance against the suit slam bidders. ðŸ˜†

A GRAND slam requires a 70% chance of success.Â Since this is very close to the odds of a 3-2 breakÂ (see below), bidding a grand slam which requires ATÂ MOST a (68%) 3-2 break is acceptable. Any grandÂ slam which requires MORE than that is to be eschewed.

The basic rule regarding suit splits is a simpleÂ one: “SUITS BREAK OFF-CENTER”. This means that ifÂ there are SIX cards outstanding the odds are AGAINSTÂ a 3-3 break. Indeed, only 36% of the time will thisÂ suit divide evenly. More than 60% of the time itÂ will divide 4-2. Remember this the next time you areÂ in a Moysian (i.e. 4-3) fit, or the next time you haveÂ AKQ10 opposite three small. ðŸ˜†

Five cards outstanding usually split 3-2. In fact,Â they will do so 68% of the time. They will break 4-1Â just less than a third of the time. “Hawaii” (i.e. 5-0)Â breaks come up about 1% of the time (unless it is BillÂ and I in a slam contract, in which case two zeros can beÂ added after the “1”).

When there are FOUR cards outstanding the odds areÂ 50% that they will break 3-1 (i.e. off-center), 40% thatÂ they will divide 2-2 (down the center), and 10% thatÂ they will split 4-0. Remember this the next time

sometime tells you “8 ever, 9 never” ! ðŸ™‚

Three cards outstanding will split 2-1 about twoÂ thirds of the time.

These percentages are combined by multiplication orÂ division. For example, a contract which required a

finesse AND a 3-2 break would be a (.50 x .68 = .34) 34%Â proposition. If a game, it would be considered SLIGHTLYÂ “anti-percentage”. Meanwhile, a contract which requiresÂ a finesse OR a 2-2 break will succeed

(.50 + [the remaining .50 / .40] = .70) 70% of the time.

Often beginners will watch their side make 12Â tricks and ask: “How can we bid that slam?” They doÂ not stop to calculate the odds of that “slam” making. If,Â say, it required two finesses and a 2-2 break it would beÂ a (.50 x .50 x .40 = .10) 10% proposition. This is NOTÂ a slam you’d want to be in! You would get NINE badÂ results for every good result!

Ward’s Maxim #271 applies here: “Good bridge isÂ always punished in the short term.”

While I don’t wish to disagree with the “Hardy Rule”Â (which states that “99% of the time percentages are WRONG”),Â I can only advise you to understand these odds and tryÂ to bear them in mind as you play and analyze each hand.

Esta entrada tambiÃ©n estÃ¡ disponible en: Spanish