Question

ricardo has 6 books written by 5 different authors, in how many ways can he arrange them on a shelf so that the 2 books by the same author are next to eachother?

Answer 1

5! There are 5 ways to have the two books next to each other. Each case has 4! permutations of the other books. 5*4!=5!=120

Answer 2

wait i made a mistake

Answer 3

multiply that by 2 to permute the two books next to each other. 2*5!=240. sorry

Answer 4

6*1*4*3*2*1=144

Answer 5

? kbetz how did you come up with that