Source: Test your Bidding
They overcall 1NT… Nil vulnerable
An opposition 1NT overcall is a gamechanger. It shows about 16-18 HCP with a stopper in the opened suit. Your objectives have shifted from a possible game investigation to just trying to obtain a plus score. Here are the rules of engagement when your RHO overcalls 1NT:
- Double is for penalties, and shows about 10+ HCP. If you do have such a hand, then your LHO must be very weak, and such hands are a nightmare for the 1NT bidder, who must play the contract out of his own hand.
- The corollary is that if you choose any other bid, you are denying 10+ HCP! In particular, a bid of a new suit does not show strength but a weakish hand with a long suit.
- Be aware that the 1NTer’s heart stopper is sitting over your partner’s hearts. This argues for caution if you have heart support but weak hearts. Indeed, if your hand is weak, then your side’s finesses are going to be mainly losing!
With these guidelines in mind, choose your bid with:
Solutions:
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(a) 
Q8643 
53 
A92 
864
Pass. You would have responded 1 to partner’s 1, but that option has disappeared. Your best bet is simply to try to defeat 1NT. (Your choice of an opening lead is a real puzzler!)
(b) Q864 53 A92 KJ104
Double. They’re in heap big trouble. You have the majority of the points and cover in all the suits. Plan to lead a heart to eventually set up winners for partner in that suit.
(c) J864 643 A972 Q4
Pass. Without the intervention, you would have raised partner to 2. But that is unwise now because 2 is unlikely to play well with any heart finesse losing. By passing here you are saying that you have a better chance of taking 7 tricks against 1NT than taking 8 tricks in a 2 contract.
(d) J843 Q106 A972 64
2. Conversely on this hand, your Q10x are well placed, sitting over RHO’s heart stopper. 2 should have good chances, and if it makes, will earn a better score than defending 1NT.
(e) KQ3 3 J109732 864
2. Shows a weakish hand with long diamonds. Partner should pass this 9 times out of 10, and on the 10th time, he should probably pass as well.
(f) 64 3 KJ932 QJ864
2NT. A curve ball. A 2NT bid here cannot logically be natural: with 10-12 HCP, you would double 1NT instead. So what else could it be but “unusual” for the minors?