North opens 1♦ with the intent of rebidding 1NT to show 15-16 HCPs and a balanced hand.

North raises 1♦  to 2♦ s with great support. Not storng enough to bid 3♦ but will rebid ♦ s in a competitive auction.

West shows the ♠ s.

North would like to bid 2NT to show values, but does not have a stop in ♠ s so just bids 3♦ s.

♦ A lot could happen with the bidding here. Though most will arrive in 3♦ 

East could have bid a pre-emotive 3♣ In position 1. Often pre-empts are done in 3♣ with only 6 cards as 2♣ is a strong bid. Positions 1 and 3 are very good for pre-empty. Some may not bid 3♣ as containing a 4 card heart suit and you risk pre-empting your partner.

After 2 passes west could open 1♠ , but some may prefer 2♠ in position 3 as partner has passed there is no hope of game and it will make it more difficult for north to bid who is likely to have the HCPs. Either way north will overcall in ♦ s.

The ♦ s will be supported by south.

1♠ is a good opening bid with the plan to rebid of NTs at the lowest level to show the  15-16 HCPs balanced hand.

No good rebid for north. 2♥ s should probably be with 9 HCPs but bidding 1NT with only a singleton in partners suit is not good. Your choice, I did not say bridge was an easy game. Over 1NT or 2♥ s 2NT from South will be passed by North.

West opens 1NT to show balanced hand 5332 and 12-14 HCPs.

East tries Stayman to find a major fit.

Wests 2♦ s denies a 4 card major.

Easts 2NTs invites West to bid 3NTs if maximum 1NT opener.

With a basic 12 HCPs  that includes 2Qs many will pass though some will be positive about the 5 card club suit as a source of tricks and will raise to 3NT.

With the lay of the cards only 1NT can be made.

Some North’s May open with 1♥ which meets the rule of 19 but not 20. The rule of 19 or 20 is the total number of points and the length of the two longest suits and is a guide whether to open. With an easy 2♦ rebid some norths will open and will do well today as south will raise.

After  a pass and 1NT by East, South can overcall with 2♠ s.

West should not overcall 3♦ s as this is normally an invitational bid and West does not have enough points.

1♠ opening from East.

West bids 2NT showing 11-12 HCPs balanced and denying 4 card support.

East preferes a suit as unbalanced so bids 3♦ s that shows 5+♠ , 4+♦ s in a hand not suitable for NTs.

West with 3 spades can bid game.

Some may end up in 3NT, but in duplicate you can make an additional trick in ♠ s so should score better.

South opens 1♠ .

Some Wests may double or bid 2♣. If bidding a double is good as West has great shape and 4 in the other major.

North in a competitive auction should probably bid 3♠ s following the law of total tricks. This says with 10 trumps between your hands the best option in the long run you should bid to make 10 tricks (bid to the level of the number of trumps held). Some may only bid 2♠. 

Some Easts may bid 1♣ , but it is a poor 11 HCPs containging 3 Qs (for more info on hand evaluation see this link)

West opens after 3 passes with 1♠ .

East responds 2NT showing 11-12 HCPs and denying support for partners suit.

West with 15 HCPs and a balanced hand can easily bid 3NT.

A difficult one to bid and to play.

Over 1♥ some souths may make it difficult with an unusual NT bid, by bidding 2NT. Showing 5+/5+ in the minors. It is a bit weak for many.

Over 1♥ west will bid 1♠ .

East bids 2♦ to show <15 HCPs and 5+♥ s / 4+♦ s

West has a difficult decision whether to bid 2 or 3♥ s. However you have a singleton in partners 2nd suit and he is unlikely to have support for ♠ s.

When you have a poor fit in other suits it is best to be cautious and bid 2♥ s. East will raise this to 3♥ s as an invitation and west will raise to 4♥ s.

This is a very difficult hand to make and most will go off. Have a play with the hand on the website. After South leads the J♠ - which is obviously a singleton. If west  takes the Ace, he must lead another ♠ to make the contract ♣ ♦ ♥ s will lead to one off! Not obvious or the likely play.

If South overcall the  1♥ with the unusual 2NT the bidding may go:

1♥  - 2NT 

Cannot bid 3♥ as partner may only have 4♥ s

A double is confusing as south has shown 5+/5+ in minors soprobably shows limited support for ♥ s and 4♠ s.

So West may bid 3♠ s which gets passed out.

If West passes North will bid 3♣ s, then it is difficult to bid.