The volcanos are always placed symetrically so that each player has them in the same positions. There are 10 squares in which they can be placed (in any of the ten squares in the row on 'your' half of the board farthest from the edge). The formula for the number of ways to choose two squares out of ten is 10!/(10-2)!x2! = 10x9/2 = 45 ways.