Your partner opens 1NT (15-17) in second seat, and it’s hard for you to believe that you have this huge hand:
Where do you go from here? If your partner has 16 or 17 high card points you should be in a grand slam (16 plus your 21 equals 37, minimum for a grand). But what if your partner opened with 15 HCP?
Holding 15 points, it’s possible that your partner opened missing the ace of clubs, in which case you want to sign off in the small slam (15+21+4 for the ace equals 40). You will find that out by using the Gerber convention.
Once you are assured that partner holds the ace of clubs, she must have at least 11 other high card points. That leaves the opponents with at most four high card points, which must come from these cards: spades K Q J, hearts Q, diamonds Q J, and clubs K J. Those four points will be from either a queen and both jacks, or two queens, or a king and a jack. It looks like you will have a good play for the grand with most of those possible combinations. Notice that your hand is bolstered by the 10 9 of clubs and the married J 10 of hearts.
But shouldn’t you just be conservative and settle for the small slam. No, you should go with the percentages. Thats what the good players will be doing, so making an overtrick in a small slam is likely to award fewer than 50 percent of the matchpoints.