What happens to F, V and E if some parts are sliced off from a solid? (To start with, you may take a plasticine cube, cut a corner off and investigate).

Case I: The given cuboid has:
(i) Number of faces (F) = 6
(ii) Number of vertices(V) = 8
(iii) Number of edges (E) = 12
We have, F + V = 6 + 8 = 14
F + V - E = 14 - 12 = 2
i.e. F + V - E = 2
or the Euler's formula is verified.
Case II: [A part is sliced off]
We have:
Number of faces (F) = 7
Number of vertices (V) = 10
Number of Edges (E) = 15
Also, F + V = 7 + 10 = 17
and F + V - E = 17 - 15 = 2
Here also, Euler's formula holds true.