Question

A one-stop flight from seattle to nyc can stop at boise, omaha, or chicago. the flight then connects to either la guardia or jfk airport, both in nyc. how many different routes are possible?

Answer 1

The first and only stop of the flight can be Boise, Omaha or Chicago. This means there are 3 possibilities where to stop. From thee the flight connects to New York City, either to La Guardia or to JFK Airport.
1 possible route: Seattle-Boise-La Guardia
2 possible route: Seattle-Omaha-La Guardia
3 possible route: Seattle-Chicago-La Guardia
4 possible route: Seattle-Boise-NYC
5 possible route: Seattle-Omaha-NYC
6 possible route: Seattle-Chicago-NYC

Or in other words: There are two airports where the flight can arrive and for each of them there are three possible routes. So, in total there are 2*3=6 possible routes.