When the game starts, Alice and Bob go into separate soundproof rooms — they cannot communicate with each other in any way. They each flip a coin and note whether it came up Heads or Tails. (No funny business allowed — it has to be an honest coin flip and they have to tell the truth later about how it came out.) Now Alice writes down a guess as to the result of Bob’s coin flip; and Bob likewise writes down a guess as to Alice’s flip.
If either or both of the written-down guesses turns out to be correct, then Alice and Bob both win as a team. But if both written-down guesses are wrong, then they both lose.
Can you think of a strategy Alice and Bob can use that is guaranteed to win every time?
(a) What is the length of the shortest path an ant could take to go from the topmost vertex to the bottommost vertex?
(b) What will be the projection on the table if there is a light source right above the cube?
(c) What would be the cross-section obtained if we slice the cube along a plane parallel to the table, passing through the midpoint of the topmost and the bottommost points of the cube?
(d) Split a large 3×3×3 cube into 27 small 1×1×1 cubes. An ant can burrow through one small cube to an adjacent small cube if these two cubes share a face. Can the ant burrow through all of the 27 small cubes, visiting each small cube exactly once? Can such a sequence have the additional property that the first and the last small cube share a face?
At every step, the magician removes two balls from the bag chosen uniformly at random and tosses them away. If the colors of these two balls were identical, he puts one white ball in the bag, otherwise he puts a black ball in the bag.
Given B and W, what are the chances that the last ball left in the bag is white?