A teacher of 6 students takes 2 of his students at a time to a zoo as often as he can, without taking the same pair of children together more than once. How many times does the teacher go to the zoo?  Select:
A) 10	B) 12	C) 15	D) 20	E) 30
Two students can be selected from 6 in 6C2 =15 ways.   Therefore, the teacher goes to the zoo 15 times.   Option 15 is answer
<result>C</result>
A teacher of 6 students takes 2 of his students at a time to a zoo as often as he can, without taking the same pair of children together more than once. How many times does the teacher go to the zoo?