[petterb]

Q7543

AJ86

What is the best way to play this suit for no losers?

[Stephen Tu]

Fairly simple to enumerate the winning/losing cases:
low to J works better if RHO has K2 or stiff K.
Running Q works better if RHO has KT2 or K92. (You are of course hooking when covered and T/9 drops on the left, restricted choice principle applies)

So one 2-2 break and one 3-1 break vs. 2 3-1 breaks. Individual 2-2 break is more likely than an individual 3-1 break by a little bit over half a percent, so low to J is best for all the tricks, double dummy defenders. Note though that running the Q is better at matchpoints though, since 4 tricks is better than 3 if the split is 4-0 onside.

Also, if defender thinks declarer may have more than 4 cds, Qxxxx in the dummy, there is some vig in that they might not cover from K2, fearing partner has singleton ace. So in many practical situations running the Q is probably better as that would be enough to cover the small double dummy edge.

[gnasher]

Small to the jack works against 3/6 of the 2-2s (~ 20%) and 1/8 of the 3-1s (~ 6%)

Leading the queen, then taking another finesse when the 10 or 9 appears on the left, works against 1/6 of the 3-2s (~ 7%) and 2/8 of the 3-1s (~ 13%).

Hence low to the jack is better.

[Stephen Tu]

gnasher, running q works against 2/6 of the 2-2s. KT and K9 doubleton onside. So it is much closer than your figures, and why running the Q may work out better in practice when K2 decides not to cover some portion of the time.

[gnasher]

Good point. I knew I should have cheated by looking it up. Using more exact figures:

Small to jack = 3/6 x 40.7 + 1/8 x 49.7 = 26.6

Running queen = 2/6 x 40.7 + 2/8 x 49.7 = 26.0