1. A reconnaissance class has 12 soldiers, including 3 telegraph operators. Now these 12 soldiers are randomly divided into three groups, with 3, 4, and 5 soldiers respectively. The probability that each group has 1 telegraph operator is $\qquad$
$-1 . \frac{3}{11}$.
Notice that, when 12 soldiers are randomly divided into three groups with 3, 4, and 5 soldiers respectively, the number of ways to do this is $\mathrm{C}_{12}^{3} \mathrm{C}_{9}^{4} \mathrm{C}_{5}^{5}=27720$. Among these, the number of ways to ensure that each group has 1 telegraphist is $\mathrm{C}_{9}^{2} \mathrm{C}_{7}^{3} \mathrm{C}_{4}^{4} \mathrm{~A}_{3}^{3}=7560$.
Therefore, the probability that each group has 1 telegraphist is
$$
\frac{7560}{27720}=\frac{3}{11} \text {. }
$$