David stands on a street corner tossing a coin. He decides he will toss the coin 10 times, each time walking 1 block north if it lands headsup, and 1...

David stands on a street corner tossing a coin. He decides he will toss the coin 10 times, each time walking 1 block north if it lands headsup, and 1 block south if it lands tails up. Find the probability that he ends up 10 blocks north of his original corner.