BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Permutation

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Master | Next Rank: 500 Posts
Posts: 165
Joined: Wed May 28, 2008 11:25 pm
Thanked: 9 times
GMAT Score:730

Permutation

by sumithshah » Tue Sep 23, 2008 9:26 pm
Carly has 3 movies that she can watch during the weekend: 1 Action movie, 1 Comedy, and 1 Drama. However, she needs to watch the Drama 3 times. Assuming Carly has time for 5 movies and intends to watch all of them, in how many ways can she do so?

6
20
24
60
120

OA is[spoiler] B
[/spoiler]
Top
Source: — Problem Solving |
User avatar
Junior | Next Rank: 30 Posts
Posts: 18
Joined: Fri Jun 20, 2008 12:04 pm

Re: Permutation

by tparekh » Tue Sep 23, 2008 11:49 pm
Look upon it from the Action (A) and Comedy (C) perspective. Imagine there are 5 time slots - "A" can take any one of the 5 slots, and "C" can take any of the remaining 4 slots. D occupies the remaining 3 slots and order does not matter. Hence the answer is 5 * 4 ?
Top
Legendary Member
Posts: 891
Joined: Sat Aug 16, 2008 4:21 am
Thanked: 27 times
Followed by:1 members
GMAT Score:660(

by 4meonly » Wed Sep 24, 2008 2:16 am
she has 5 positions to put A, B and C
C must be repeated 3 times
so we have ABCCC
total combinations - 5!
C is repeted 3 times, so we should divide 5! by 3!
Because ABC1C2C3 is the same as ABC2C1C3

5!/3!= 20

B
Top
Post new topic Post Reply
• Page 1 of 1