Rules

Question 1

Rule of Seven

Answer 1

How is it used? Declarer adds together his own cards in the suit and dummy’s cards in the suit and deducts the total from SEVEN.
The number left is the number of times to hold up before playing your singleton stopper.
Purpose: you are trying to exhaust one of the enemies of their cards in the suit when the suit is splitting badly (if it is evenly split, rule of seven does not help)
Who uses it? declarer in NT contract
When? in a NT contract when you are declarer and worried about a particular suit and when to play your singleton stopper in the suit.

Question 2

Rule of Eleven

Answer 2

How is it used? As defense when partner has led fourth highest card as the opening against a NT contract. Subtract the pip on the card from eleven. The answer gives you the number of cards higher than the card led in the other three hands.
Purpose: To help you choose a lead as eg. if partner led a 4, giving seven cards in the other three hands (ignore the hand of the lead), and you can see 3 in dummy and 3 in own hand, that means declarer as 1 card.
Who uses it? responder to leader on first hand
When? first round when partner has opened fourth highest.