Bidding : 2C (N) - 3D (S) - 6NT (N)
South, with 8+ points, must bid 3D. The 2D response is for all weak 0-7 pts hands only.
North can also bid 4NT Blackwood first to check out South's Ace and King. 6S or 6D are possible contracts too of course, but in Duplicate bridge the NT contract will receive a top score.

Opening Lead : Queen of Clubs (E) = top of a solid sequence

Declarer (N) counts 11 sure winners : 6 Spades, A of Hearts and A K of Diamonds and Clubs. Dummy's Diamonds can provide the extra winner, provided the enemy cards are split 3-2. If not Declarer can still try the Heart finesse for the extra trick required.

Declarer Play
2C opening bid   -   Duck to preserve an entry
Declarer wins the opening lead with his Club King, then leads a small Diamond from his hand and ducks in Dummy. West wins with the Jack.
At trick 3 West leads another Club, returning Partner's lead, which is won by Declarer's Ace.
Declarer now leads his last remaining Diamond to Dummy's Ace which wins. Both Opponents have followed suit so the contract is safe. At trick 5 Dummy leads the Diamond King on which East's Queen drops. Declarer discards his Heart Queen and small Club on the next two Diamond tricks lead and won by Dummy.
All remaining cards in Declarer's hand (Ace of Hearts plus six Spades) provide the remaining tricks, a total of 12.

Score = 40 + 5 x 30 trick pts + 800 bonus pts = 990 pts total

Bidding : Pass (E) - Pass (S) - 1C (W) - 1S (E) - 4S (W) - Pass (E)
With 20 points West can not open NT but must bid a suit. East shows 6+ points which is enough for West to go to Game (also showing 19-20 pts). (With extra values East could still have continued to Slam).

Opening Lead : Queen of Hearts (S) = top of a solid sequence

Declarer (E) counts 5 possible losers : two in Spades, one in Hearts and two in Diamonds. He must avoid the trump Ace and take a chance on a finesse in Diamonds or make a throw in play.

Declarer Play
Duck to drop an Honour   -   Throw in for an end play
Dummy wins the opening lead with the King of Hearts.
Declarer notices that Dummy holds K 9 in Spades. This could be useful for a second round deep Spade finesse in case the Jack or 10 falls in the first round of Spades. He therefore leads a small Spade from Dummy to his Queen, which wins as North and South both play low. North is now marked with the Spade Ace. At trick 3 Declarer leads a small Spade, South plays the 10, Dummy ducks and North drops his Ace which wins.

North leads a Heart at trick 4, returning Partner's lead, which is won by Dummy's Ace. Declarer now draws the last enemy trump with Dummy's Spade King, then plays three rounds of Clubs stripping the suit in both hands.

Declarer is now ready for the throw in and at trick 9 plays the last remaining small Heart in both his and Dummy's hand. South wins the trick but now is end played.
A Heart or Club lead will give Declarer a ruff and sluff, discarding a Diamond in one hand. A Diamond lead instead will give Declarer a free finesse, making two Diamond tricks, no matter how the cards fall. He makes a total of 10 tricks.
Declarer could of course have finessed the Diamonds himself, but might have guessed wrong losing two tricks. The throw in play ensures the 100% certain outcome of the necessary 2 Diamond winners.

Score = 4 x 30 trick pts + 300 bonus pts = 420 pts total

Bidding : Pass (S) - Pass (W) - 1C (N) - 2H (S) - 6H (N) - Pass (S)
With only 12 pts South passes in 1st or 2nd position. North with 21 points can not bid NT. South Jump shift response shows a "maximum pass" plus 5 Hearts, upon which North goes to Slam.

Opening Lead : Jack of Spades (W) = top of a solid sequence

Declarer (S) counts 2 possible losers One Heart loser if the trumps break 3-1 or worth with no singleton Q, plus one Diamond loser.

Declarer Play
Throw in play via a trump loser
Declarer wins the opening lead with Dummy's Spade Queen, then plays two rounds of trumps winning with Dummy's Heart Ace and King. On the second round East shows out, which means that West will win a sure trick with his trump Queen which is now high.

Declarer therefore prepares for a throw in. He first (at trick 4) leads a small Club from Dummy to his King, then returns a small Club to Dummy's Ace. Dummy then (trick 6) leads his last remaining Club which is ruffed by Declarer.

At trick 7 Declarer leads his Spade Ace, followed by his last Spade to Dummy's King. The two black suits are now stripped in both hands. At trick 9 Dummy leads a small trump, won by South's Heart Queen, who is now end played.
A lead in Spades or Clubs will give Declarer a ruff and sluff, discarding a Diamond in one hand, while a Diamond lead will provide a free finesse, ensuring three Diamond tricks. Either way Declarer wins a total of 12 tricks.

Score = 6 x 30 trick pts + 800 bonus pts = 980 pts total

Bidding : 1S (W) - 3S (E) - 4NT* (W) - 5C (E) - 5NT* (W) - 6H (E) - 6S (W)
* Blackwood Convention : East shows no Ace and 2 Kings

Opening Lead : King of Clubs (N) = top of a solid sequence

Declarer (W) counts 2 possible losers : one in Hearts and one in Clubs. There is a two-way finesse position in the Hearts. Which one will be the right one ?

Declarer Play
Blackwood Convention   -   Throw in for an end play
Declarer wins the opening lead with his Club Ace, then leads two rounds of Spades, drawing all enemy trumps.
At tricks 4, 5 and 6 he strips both hands of Diamonds, then (trick 7) throws in the Opponents by playing a low Club in both hands. North wins the trick, but is now end played.
A Diamond or Club lead will give Declarer a ruff and sluff, discarding a Heart in one hand. A Heart lead will set up a free finesse against the Queen, producing 3 Heart tricks for Declarer. Either way he wins 12 tricks in all.

Score = 6 x 30 trick pts + 1250 bonus pts = 1430 pts total