Answers:
1.
Hint: You have one sure trick. What is your best chance for a second trick?
Answer: As long as you get in with your
♥A, you will have a spade trick ready to take if you lead the
♠K on opening lead, and that is the recommended lead.
This seems like a pretty certain set - so why didn't my auction have West doubling 6NT?
Two reasons.
First, North, with a void in hearts, may think you're doubling on the
♥AK and run to 7C, and a successful ruffing finesse against your
♥A may be all he needs to bring it home. (South, the dummy in clubs, will lead high hearts and North will discard until you play your ace, making dummy's heart suit high.)
Second, you have a lot of high cards on this auction so it's likely the opponents have extra distribution (i.e. a 7-card club suit.) When you lead your
♠K and South wins the
♠A and plays seven rounds of clubs, you are in big trouble if South has four diamonds and partner has no help. No other lead would have helped though, so the
♠K lead virtually sets the contract whenever it can be set.
2.
4H was a transfer to spades; 4NT was ace-asking; 5H showed two.
Hint: Do you realize you have a trump trick?
Answer: You should have a trump trick and the auction sounds like there is no heart void so lead the
♥A. If you fail to lead it, you may see declarer discard dummy's hearts on good clubs in his hand and you could get only one trick.
3.
Hint: Are you likely to score any length tricks with low cards?
Answer: Against 1NT-3NT, you would lead fourth from your longest and strongest, hoping that partner has some help in hearts to let you use your little hearts to take tricks. Against 6NT, you are unlikely to score any tricks with little hearts. Declarer and dummy are likely balanced and declarer may have to try to win heart tricks himself to make 6NT, and you may score your
♥K and/or
♥J as long as you don't lead hearts yourself. Make declarer play for twelve tricks while giving him nothing. The
♠10 appears to be the safest lead, unlikely to give declarer anything that he can't get himself. The diamond and club leads have some chance of finding partner's queen for declarer - a queen that may take a trick on defense if declarer is left to his own devices.
4.
Hint: What is likely to happen if you lead passively?
Answer: On the last hand, with declarer expected to have balanced hands, you defended passively and hoped declarer would give the defense two tricks. Let's think about declarer's plan on this hand. Declarer is likely to try to take many club tricks and many heart tricks. If declarer can do that without losing the lead, he should have bid seven. If declarer has to lose two tricks in those suits, it makes little difference what you lead. However, if declarer has to give up the lead exactly once to establish his club and heart winners, then declarer will have twelve tricks for the taking once he gives up that trick, and the defense had better have set up a second winner when the defense gets in that one time.
The best chance to set up a second winner is to hope partner has the
♦Q and lead a diamond. Partner could have the
♠KQ instead but it's a lot more likely that partner has one needed card than two. The recommended lead is the
♦4.
5.
Hint: Did partner offer any help?
Answer: As JLilly pointed out, partner suggested a diamond lead. If I held the
♥KQJ, I might ignore his suggestion (figuring that he was just showing me where his only card was) but here I have no reason not to respect his suggestion. Lead a diamond.
6.
Hint: Did partner offer any help? Could he have?
Answer: Here, we have no clue except for the fact that partner did not suggest a diamond lead, making the heart lead a better choice since there is some chance that partner would have suggested a heart lead given the opportunity. I chose hearts rather than clubs because dummy may have a club suit that declarer will need to establish (based on the bidding.)