Source: [ilink url=»http://www.acbl.org/»]2006 ACBL Bulletins[/ilink]
A capable declarer will succesfull guess the location of a relevant queen at least 75% of the time by constructing the defenders’ hands, using clues from the bidding and play. Try the following problems.
West leads the 
A and continues with the Q. Dummy’s king wins, and you pass the 
J to West’s king. He cashes the J -East follows – and exits with a trump. You draw trumps, finding that West had three, and finesse with the 
Q, winning.
When you cash the A and ruff a heart, West plays the king and jack. Who has the the 
Q?
West is known to have had balanced distribution and has shawn 14 PH: K, KJ and A Q. If West had the Q, he’d have opened 1NT, so East has the queen.
West leads the 2. You try dummy’s queen, but East produces the king and returns a diamond. The defenders cash four diamonds in all, as you discard two clubs, from dummy and a club from your hand. West then leads a heart. What now?
Suppose you cash your heart and spade winners. All follow to the hearts, and West discards a heart on the third high spade. How do you play the clubs?
West started with two spades, four hearts and four diamoods, hence three clubs. Cash the K and let the J ride.
West leads the 2. You play low from dummy and East wins with the jack and leads a trump. West takes the ace and leads the Q, winning, and a third club. East covers dummy’s king. You ruff, draw trumps, take the K, A and ruff dummy’s
last spade. East follows with the 3, 4 and 8. West contributes the 2, 9 and jack. Who has the Q?
You can infer that West has no more spades. If his spades were Q-J–9–2 or J-10-9-2, he’d have led a spade from his sequence instead of a club from a broken queen-high suit. If West started with three spades, two hearts and (from the opening lead) four clubs, he had four diamonds to East’s two. The odds favor playing West for the Q.