Sarah works in an office at the corner of Main and Center Streets. She lives on the corner of 4th Avenue and E Street (see the map on the attachment). On her walks home from work she likes to try as many different routes as possible without making her trip any longer than needed. She has noticed that there are many different routes that will take her home with a walking distance of 9 blocks -- she merely chooses whether to go north or east at each intersection, taking care to never go north of 4th Avenue or east of E Street.
Your task is this: find the number of different routes that Sarah might use.
Here's a slight hint that might save you a lot of tedious counting: Sarah must travel east 5 blocks and north 4 blocks -- is there a formula you could use to count the number of routes if instead it was m blocks east and n blocks north?
ok we had this in school
she can go 4 times north, and 5 times east.
first point she can choose two ways, east or north
till she chooses either 4 times north or 5 times east, simple
Linear Mode
