phone interview: (1) 3x3 large square, the surface is painted in red. After cutting into 27 pieces, just take one piece and throw it on the table. Five sides are white and white. Ask the probability that the last face is red. (2) X = the sum of 100 rolls of dice, Y = the number of heads of 600 coin flips, ask Pr (X>Y) (3) N points randomly in a circle. The probability that all of them lie in a semicircle