This football consists of 12 black pentagonal leather blocks and 20 white hexagonal leather blocks. These skins are made up of 90 faces. Q: How many faces are connected by two white skins?

Ideas:

A ***90 faces. Black pentagons are unconnected, so the sides connected with them are *** 12X5.

Answer:

12x5 = 60 (piece)

90-60 = 30 (pieces)

A: Omit.