Consider a young man who is waiting for a young lady, who is late. To amuse himself while waiting, he decides to take a walk under the following set of rules. He tosses a coin (which we may assume is fair). If the coin falls heads, he walks 10 yards north; if the coin falls tails, he walks 10 yards south. He repeats this process every 10 yards and thus executes what is called a "random walk." What is the probability that after walking 100 yards he will be (i) back at his starting point, (ii) within 10 yards of his starting point, (iii) exactly 20 yards away from his starting point.