119 = 11!9!2!=11 10 9 8 7 6 5 4 39 8 7 6 5 4 3 2 1=55.

jmc

counting and probability junior

Problem

Compute

(9 11)

Solution

(9 11) = \frac{11 !}{9 ! 2 !} = \frac{11 \times 10 \times 9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3}{9 \times 8 \times 7 \times 6 \times 5 \times 4 \times 3 \times 2 \times 1} = 55 .

Final answer