This deal is from the first match of Tollemache qualifying competition earlier this month.
Alan Mould (North) and Rodney Lighton (South) bid as above.
Two notrump showed a game forcing raise with four spades, three hearts was a second suit. Now three spades showed a balanced hand, not quite minimum since he had good controls in the minors. Four diamonds was a shortage, at this point South felt he didn't have enough to progress beyond game, but when North tried again with five hearts, South re-evaluated and showed his club control. North made a grand slam try with six hearts (Alan later thought this was a bit too ambitious) and Rodney bid the grand on the basis of his good controls, trump queen and doubleton heart.
With the spades 2-2 and the hearts breaking reasonably there was little to the play.
Of the 32 tables in play seven bid the grand slam, 22 the small slam and three tables played in game.
The question is whether this is a good grand slam or not.
A grand slam needs to make about 60% of the time for it to be good odds at IMPs, providing you are sure that small slam is going to be bid in the other room.
Here (as shown by the results) it is likely that at least small slam will be bid.
A grand will make if spades are 2-2 (40%) and hearts are 4-2 or better (84%), or spades are 4-0 (10%) and hearts are 3-3 (36%) or if spades are 3-1 (50%) and hearts are 3-3 (36%).
The tricky calculation is when spades are 3-1 and hearts are 4-2. Grand will make now most of the time if the long spades are with the long hearts or if East has three spades and two hearts.
I calculate all this to be an overall 65-70% of the time, so the grand is a good proposition.