clockwise or counterclockwise
possible movement combinations are: 2^3 = 8

For a collision-free scenario, all ants must move in the same direction:

2 ways :
 -> All move clockwise 
 -> All move counterclockwise
Thus, there are 2 collision-free cases out of 8 total cases.

P(no collision)= 2/8=0.25=25%
