Rule of 11

The rule of 11 can help you to gather more information if opposition have lead 4th highest against a no trump contract. It is useful for both declarer and the partner of the opening leader.

How does it work?

Firstly you need to be pretty sure that opposition are leading 4th highest. If you are in no trumps and opps lead a middling card then this is likely the case.

Take the value of the lead card away from 11
The result is the number of cards higher than the lead in the other 3 hands (not the lead hand)
By counting the higher cards in your hand and dummy you can work out what the remaining hand must have

Example

North is playing this hand in 3NT and East leads the 8 of hearts.

11-8=3 This means there are 3 cards higher than the 8 between the North, South and West hand.

Imagine you are North. You can see you own hand and dummy.

Between their own hand and dummy, declarer can see the K,J,9 of hearts. This accounts for all 3 higher cards.

This tells North that West cannot have a high heart here. If they play small from South then they can win the 9 of hearts at trick 1.