Question 748152
there are 3 airports. one flight flies from one airport to each of the other airports every day. how many flights are there in each day
<pre>
Each flight has an AIRPORT OF DEPARTURE and an AIRPORT OF ARRIVAL.  You can
choose the AIRPORT OF DEPARTURE in 3 ways and for everyone of those 3 ways,
there remain 2 ways to choose the AIRPORT OF ARRIVAL.  That's 3×2 or 6 ways.  


This is a permutation because ORDER MATTERS!  The order of going FROM airport A
TO airport B is different from reversing the order and going from Airport B to
Airport A.  ORDER MATTERS, so it's P(3,3) = 3! = 3×2×1 = 6.   They are

1. Airport A to Airport B
2. Airport A to Airport C
3. Airport B to Airport A
4. Airport B to Airport C
5. Airport C to Airport A
6. Airport C to Airport B 

Edwin</pre>