Deal 10
 
  3NT
♠ J 6 4
9 8
A 5
♣ A J 10 7 4 2
 
 WEST  NORTH  EAST  SOUTH
1NT
pass3NTpasspass
pass

The bidding has been as shown.
Partner led the 5, dummy played the 8 and it is your play.

When you have made your choice click NEXT .

5

♠ 9 7 3
A Q 7
J 10 8 7 3
♣ K 6
 


 

 
Deal 10
 
  3NT
♠ J 6 4
9 8
A 5
♣ A J 10 7 4 2
  Play the Q.

The Rule of Eleven tells you there are 6 cards in North, East and South that are higher than the 5. You can see 5 of them, so that leaves just one of them for South.

West cannot have all three of the outstanding honors, because from K J 10 x x his correct lead would be the Jack.
So you can deduce that South must hold exactly one of K, J, or 10.

If his honor is not the K then it won't matter whether you play A or Q to the first trick; you will win your two top cards and then play your small one back to West.

So assume South actually holds the K x x.
If you play the A to trick one, then lead Q, South will hold up on the second trick, and win the third . Then, when you win your ♣K you will not have a to return to partner and declarer will make the contract.

So what happens if you play the Q at trick one?
South could still make the contract by holding up, but he will be afraid to do so. After all, from his perspective it looks like West probably holds the A and he will be afraid of losing the first 5 tricks, perhaps even when the ♣K finessing is working!

 Deal 11 
♠ K 8 5 2
J 10 6 5 2
6 4
♣ 9 3
♠ 9 7 3
A Q 7
J 10 8 7 3
♣ K 6
  ♠ A Q 10
K 4 3
K Q 9 2
♣ Q 8 5