934. Three classmates bought 13 pies, with Kostya buying half as many as Tolya, and Volodya buying more than Kostya but less than Tolya. How many pies did each of them buy?
Let Kostya buy $x$ pies, and Volodya $-y$. Then Tolya bought $2 x$ pies. We get a mixed system, consisting of an equation and an inequality:

$$
\left\{\begin{array}{l}
3 x+y=13 \\
x<13
\end{array}\right.
$$

Solving this system of inequalities, we get:

$$
2 \frac{3}{5}<x<3 \frac{1}{4}
$$

Then $x=3, 2 x=6$. Let's find $y$:

$$
3 x+y=13, \quad 9+y=13, \quad y=4
$$

Let's check if the inequality $x<y<2 x: 3<4<6$ holds.

Therefore, the inequality holds.

Answer: $3,4,6$.