Brain Teasers

1. Logic Puzzles (stamps): The Grand Master takes a set of 8 stamps, 4 red and 4 green, and loosely affixes two to the forehead of each of three logicians A, B, and C, so that each logician can see all the other stamps except those two in the Grand Master's pocket and the two on her own forehead. He asks them in turn if they know the colours of their own stamps. Their answers are:
A: "No."
B: "No."
C: "No."
A: "No."
B: "Yes."
That is, after one round of answers, in the second round, B says that she knows the answer. What colour stamps does B have?

2. Wired Equator: The circumference of the Earth is approximately 40,000 km. If we made a circle of wire around the globe, that is only 10 meters (0.01 km) longer than the circumference of the globe (40000.01 km), how much gap would there be between the wire and the ground? Would it be big enough for a flea, a mouse, or even a man to creep under it?