A decagonal based pyramid will have 11 faces, 11 vertices and 20 edges
If the prism is based on regular decagons and it is a right prism, all 12 faces.
12 faces 20 vertices 30 edges
Edges = 30 Faces = 12 Vertices = 20
20
20 edges, 11 vertices (corners) and 11 faces.
Vertices: 20 Edges: 30 Faces: 12
19 * * * * * Actually it is 30 edges. Ten around each of the decagonal faces, and ten more connecting the corresponding vertices of the two decagons.
Seven. The lateral faces are usually all rectangular.
12 faces * * * * * Correct as far as it goes, but incomplete. 20 vertices 30 edges
Not sure what a decagonal is. Since the question refers to faces, edges and vertices, it may be assumed that the object in question is 3-dimensional. A decagon certainly is not, so decagonal cannot be a mistaken name for a decagon.
A pyramid has one more corner and faces than the number of sides in its base; thus a decagonal pyramid has 10 + 1 = 11 faces and corners. A pyramid has twice as many edges as sides in its base; thus a decagonal pyramid has 2 X 10 = 20 edges.