There are b cities. What is the number of airlines that connected 2 different cities (airline from city A to city B is different with airline from city B to city A)?  Select
A) n(n-1)
B) n(n+1)
C) n(n-1)/2
D) n(n+1)/2
E) b(b-1)
First of all, the possible number of airlines is b. Then, the possible number of airlines departing from one city to another becomes (b-1). Hence, the answer is b(b-1), which makes b(b-1)
<result>E</result>
There are b cities. What is the number of airlines that connected 2 different cities (airline from city A to city B is different with airline from city B to city A)?