In a country there is a total of 20 airports. Each one of theseairports are linked to all the others, either through direct orindirect (ie. connecting) flights. There are at most two direct flightsamong any randomly chosen three airports.
What is the maximum possible number of direct flights among these 20 airports?
Note: If there is a flight between A and B, it can be used in both directions and it will be counted as one flight.