求解

susannuaa1

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The figure shown represents a board with 4 rows of pegs, and at the bottom of the board are 4 cells numbered 1 to 4.  Whenever the ball shown passes through the opening between two adjacent pegs in the same row, it will hit the peg directly beneath the opening.  The ball then has the probability 1/2 of passing through the opening immediately to the left of that peg and probability 1/2 of passing through the opening immediately to the right.  What is the probability that when the ball passes through the first two pegs at the top it will end in Cell 2?

A.    1/16
B.    1/8
C.    1/4
D.    3/8
E.    1/2