PIE=Principle of Inclusion and Exclusion

4. Gridtown USA, besides having excellent donut shops, is known for its precisely laid out grid of streets and avenues. Streets run east-west, and avenues north-south, for the entire stretch of the town, never Suppose you live on the corner of 3rd and 3rd and work on the corner of 12th and 12th. Thus you must (a) How many different routes can you take to work, assuming you want to get there as quickly as (b) Now suppose you want to stop and get a donut on the way to work, from your favorite donut shop curving and never interrupted by parks or schools or the like travel 18 blocks to get to work as quickly as possible. possible? Explain on the corner of 10th ave and 8th st. How many routes to work, stopping at the donut shop, can (c) Disaster Strikes Gridtown: there is a pothole on 4th ave between 5th st and 6th st. How many (d) The pothole has been repaired (phew) and a new donut shop has opened on the corner of 4th ave you take (again, ensuring the shortest possible route)? Explain routes to work can you take avoiding that unsightly (and dangerous) stretch of road? Explain. and 5th st. How many routes to work drive by one or the other (or both) donut shops? Hint: the donut shops serve PIE