Liz is standing on the real number line at position 0. she rolls a die repeatedly. if the roll is 1 or 2, she takes one step to the right (in the positive direction). if the roll is 3, 4, 5 or 6, she takes two steps to the right. let xn be liz’s position after n flips of the coin. estimate the probability that x90 is at least 160.