This conundrum about slam bidding was written by Barbara Seagram together with David Bird and was originally published in the book, Bidding at Bridge - A Quizbook - you can find out all about it further down the page.
When two balanced hands face each other, you need around 33 HCP to bid 6NT and 37 to bid 7NT. Auctions such as INT - 6NT are commonplace, with the responder merely adding his points to those shown by the opener. When responder needs an upper-range opening to justify bidding 6NT, he can invite a slam by responding 4NT (this is not Blackwood when it is a raise of a natural notrump bid):
East holds 17 HCP and would like his partner to play in 6NT if he has 16 or 17 HCP opposite. He passes this message by responding 4NT. West has a maximum
17 HCP and accepts the try, raising 4NT to 6NT. There are eleven tricks on top and several good chances of setting up a twelfth trick. (At an early stage declarer will duck a round of spades to test for a 3-3 break in that suit.)
Let's see what would happen if West did not hold quite such a good hand.
West has a minimum INT opening of 15 HCP and rejects the invitation. There are nine tricks on top and an easy tenth trick can be established in hearts. 6NT would require a considerable amount of luck and would not be a good contract.
From the deals we have seen, you will realize that slam bidding is not a precise art. When a slam is likely to be a good prospect, take the plunge and bid it.
Sometimes making the slam will be easy. Other times it may need a finesse or a favorable lead. Occasionally the slam may prove to be a bad one on the cards that partner happens to hold. Don't let the occasional failure prevent you from bidding slams in future.
This book gives the near-beginner a chance to practice the principles on which sound bidding is based, from the opening bid onward. This is not just a series of problems, however. Each section contains a brief introduction to its topic, and the ideas are reinforced with carefully explained solutions and helpful tips throughout. Bridge teachers and students will find this book invaluable.