thread: Barrons 2400 Question View Single Post
 02-16-2007, 10:44 PM #1 OBrienUM97 Member   Join Date: Aug 2006 Posts: 330 Barrons 2400 Question In the permutations combinations chapter of the 2400 book (page 222 if you have it near you) says on the combinations, if order is irrevelevant you divide number of combinations by r!, which makes sense since order is irrelevant. but then at the end of the chapter in the review questions (number 10 page 230) it says to times the total number of combinations by r! heres what it says for those of you who don't have it... calculate number of 3 person committees made up of 6 willing people. so you would do 6x5x4 to get 120, and since order doesn't matter, it says you must divide by 3x2x1. on the review test it says... 6 chairs are placed in a row to seat 6 people. how many arrangements are possible if two of the people insist on sitting next to eachother? so that means 4 seats and 4 people are up for different combos, so 4x3x2x1 gives you 24, and since there are 5 pairs of seats in which the two people who would be sitting next to eachother would be, you times 24 by 5 to get 120. Then it says because of the fact that the two people could be sitting in any order, you multiply by 2. can someone explain to me the difference in these two processes? they appear to be asking you the same thing in both, but they do them in a manner that suggests otherwise....yea i'm pretty confused...help please... Reply