Source: 2006 ACBL Bulletins
Test your queen-placing in the following problems. Assume IMP scoring.
West leads a low diamond, and East wins with the jack. Cashes the 
A and K and leads the 
K. You ruff. Who has the 
Q?
East had the A, K and A, K and J. That’s 15 points. and he is also marked with a club honor. Since if West had the 
K Q, his opening would have been a high club. So West has the Q. East should have been less forthcoming about his diamond holding. If he leads the A at the second trick. South won’t be sure which defender has the king.
West leads the 2, and East takes the queen and ace, cashes the A and exits with a heart.West follows. You continue with a diamond to the ace, both defenders playing low. On the next diamond East plays low again. Who has the queen?
A count of high-card points is inconclusive. East had the A Q and A but could have opened with either the K or with the Q and J. Instead, draw an inference from the defense. If West had a singleton diamond, he could have beaten the contract by leading it. When East got in with the A, he’d give West a diamond ruff; and the defense would take two spades. Since even an inexperienced West would have led a side singleton, especially from a weak hand, go up with the K, expecting West to have held Q 7.
West leads the 2, dummy plays low, and East wins with the jack and shifts to the J. How do you play the trumps?
East has the A J and J, and you must assume he has the A so, place West with the Q since East didn’t open.