11. From May 1 to May 3, the school plans to arrange six leaders for duty, requiring each person to be on duty for 1 day, with two people scheduled each day. If among the six leaders, A cannot be on duty on the 2nd, and B cannot be on duty on the 3rd, then the number of different ways to arrange the duty schedule is $\qquad$ kinds.
11.42.

Divide into two categories:
(1) If A and B are on duty on the same day, then they can only be scheduled on the 1st, with $C_{4}^{2}=6$ ways to arrange them.
(2) If A and B are not on duty on the same day, there are $\mathrm{C}_{4}^{1} \mathrm{C}_{3}^{1} \times 3$ $=36$ ways to arrange them.
Therefore, there are a total of 42 methods.