A polyhedron has faces that all either triangles or squares. No two square faces share an edge, and no two triangular faces share an edge. What is the ratio of the number of triangular faces to the number of square faces?
1. Let \( s \) be the number of square faces and \( t \) be the number of triangular faces.
2. According to the problem, no two square faces share an edge, and no two triangular faces share an edge. This implies that each edge of the polyhedron is shared by one triangular face and one square face.
3. Each square face has 4 edges, and each triangular face has 3 edges. Since each edge is shared by one triangular face and one square face, the total number of edges contributed by the square faces must equal the total number of edges contributed by the triangular faces.
4. Therefore, the total number of edges contributed by the square faces is \( 4s \), and the total number of edges contributed by the triangular faces is \( 3t \).
5. Since these edges are shared, we have the equation:
   \[
   4s = 3t
   \]
6. To find the ratio of the number of triangular faces to the number of square faces, we solve for \( \frac{t}{s} \):
   \[
   \frac{t}{s} = \frac{4}{3}
   \]
7. Therefore, the ratio of the number of triangular faces to the number of square faces is \( 4:3 \).

The final answer is \(\boxed{4:3}\).