Question

Keller wants to give his friend 2 books. He can choose books on subjects from fiction, history, computers, science, general knowledge, and art. How many combinations of 2 different subjects are possible?

8
15
12
30

Answer 1

15

Explanation:

Pat, Jo, Al, Dan

Pat, Al, Dan, Jo

Pat, Dan, Jo, Al

Pat, Jo, Dan, Al

Pat, Al, Jo, Dan

Pat, Dan, Al, Jo List all permutations beginning with Pat.

Jo, Al, Dan, Pat

Jo, Dan, Pat, Al

Jo, Pat, Al, Dan

Jo, Al, Pat, Dan

Jo, Dan, Al, Pat

Jo, Pat, Dan, Al List all permutations beginning with Jo.

Al, Dan, Pat, Jo

Al, Pat, Jo, Dan

Al, Jo, Dan, Pat

Al, Pat, Dan, Jo

Al, Dan Jo, Pat

Al, Jo, Pat, Dan List all permutations beginning with Al.

Dan, Pat, Jo, Al

Dan, Jo, Al, Pat

Dan, Al, Pat, Jo

Dan, Jo, Pat, Al

Dan, Pat, Al, Jo

Dan, Al, Jo, Pat List all permutation beginning with Dan.

There are 24 ways for Pat, Jo, Al, and Dan to finish in first, second, third, and fourth place in the contest.