This mathematical concept originated back in the days of the game of Whist, and to which no name can be attached. It is similar to their cousin concepts:

1. the Rule of Eleven, which may determine the play of a card by partner, who knows that the lead card is the fourth highest card down as per partnership agreement and
   
2. the Rule of Twelve, which may determine the play of a card by partner, who knows that the lead card is the third highest card down as per partnership agreement.

The Rule of Ten states that the lead is the fifth highest card and that the partner subtract the number of the card from the number 10, and the result obtained is the number of highercards than the one led in all of the other three hands.

The following illustration should clarify this concept. The contract is 4, the declarer is South, and the lead is 3:

Declarer:

South

Contract:

4 Spades

Vulnerability:

None

Lead:

3 of Hearts
  Click here to continue reading