Youngman who is waiting for a young lady decides to walk under the following set of rules. hle tosses a fair coin. if the coin falls heads, he walks 10 steps no

youngman who is waiting for a young lady decides to walk under the following set of rules. Hle tosses a fair coin. If the coin falls heads, he walks 10 steps north; if the coin falls tails, he walks 10 steps south. What is the probability that after walking 100 steps he is: () back at the starting point, (11) 20 steps from the starting point, and (i1) 40 steps from the starting point