Deal 7
 
  3NT
OL: Q
♠ J 8
9 6 2
K Q 10 9 4
♣ 9 7 5
 
 WEST  NORTH  EAST  SOUTH
2NT
pass3NTpasspass
pass

You are East. The bidding has been as shown.
Partner led the Q, you played low and South won the A.

South now plays the J on which West plays the 2.
What do you play now, and what is your plan.

When you have made your choice click NEXT .

Q
2
♠ A 10 5 2
8 5 3
A 7 3
♣ J 6 2
 
A
J
 

 
Deal 7
 
  3NT
OL: Q
♠ J 8
9 6 2
K Q 10 9 4
♣ 9 7 5
  Play the 3 and when South plays another win with your A.

North hoped his suit would provide enough tricks to make the game.
You can see that there is no entry to the North hand EXCEPT in s, so you want to win your A on the trick that South plays his last .
How can you tell which trick that is?

Only by watching what West plays. On the J West played the 2, a low card signaling that he held an ODD number of s.
ODD must be either one or three so when he followed to the next you know he started with three.
A little bit of counting tells you that South started with the doubleton Jack, so you want to win the second trick.

This defense holds South to one tricks, if you had let him win the second one he would have had 9 tricks.

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