Target Test Prep 20% Off Flash Sale is on! Code: FLASH20

Redeem
Target Test Prep
5-Day Free Trial
5-day free, full-access trial TTP

Available with Beat the GMAT members only code

MORE DETAILS
Target Test Prep
Magoosh
Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

MORE DETAILS
Magoosh

5 people run a race and

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 29
Joined: Thu Sep 25, 2008 5:11 pm

5 people run a race and

by netcaesar » Mon Sep 07, 2009 1:38 pm
5 people run a race and none of them arrives at the same time. In how many ways can the race end with Bob ahead of Marge?

OA is 10
Top
Master | Next Rank: 500 Posts
Posts: 175
Joined: Mon Feb 09, 2009 3:57 pm
Thanked: 4 times

by tom4lax » Mon Sep 07, 2009 2:00 pm
I would actually think that it's 60.

Total ways the race can finish is 5! = 120. Now divide by two because whatever order of Bob and Marie, only one of them is valid.

How did you arrive at 10?
Top
Junior | Next Rank: 30 Posts
Posts: 29
Joined: Thu Sep 25, 2008 5:11 pm

by netcaesar » Mon Sep 07, 2009 2:42 pm
5!/2!3!
Top
Master | Next Rank: 500 Posts
Posts: 175
Joined: Mon Feb 09, 2009 3:57 pm
Thanked: 4 times

by tom4lax » Mon Sep 07, 2009 2:51 pm
Whats your logic behind 3!2!?
Top
Senior | Next Rank: 100 Posts
Posts: 77
Joined: Sun Jun 21, 2009 10:25 am
Location: Germany
Thanked: 7 times

by Nermal » Tue Sep 08, 2009 12:04 am
I also calculated it the way tom4lax did.

What came to my mind afterwards was:
Does "Bob ahead of Marge" mean that he finishes directly before Marge does or could it also be that Bob finishes first and Marge last?
Top
Junior | Next Rank: 30 Posts
Posts: 29
Joined: Thu Sep 25, 2008 5:11 pm

by netcaesar » Tue Sep 08, 2009 6:54 am
Sorry, you are right.
If there are 120 combinations, in half of them Bob is ahead of Marge, so the answer is 60.
Top
Junior | Next Rank: 30 Posts
Posts: 12
Joined: Mon Jul 07, 2008 7:28 am

by txeconomist » Thu Sep 10, 2009 2:00 pm
If it doesnt matter where people other than Bob and Marge place, then its 10 I guess.

BMMMM
XBMMM
XXBMM
XXXBM
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 166
Joined: Fri Apr 03, 2009 11:16 pm
Location: India

by Mayur Sand » Thu Sep 10, 2009 7:17 pm
My solution is following,
Lets suppose following are finished positions
p1,p2,p3,p4 ,p5 . Now If Bob came at p1 then Marley can come at p2,p3,p4,p5 which means 4 ways , similary when Bob comes at p2 then Marley can come at p3,p4,p5 3 ways
so it should be 4*3*2*1 = 24 ways

Let me know my mistake here
Top
Master | Next Rank: 500 Posts
Posts: 113
Joined: Thu Jul 16, 2009 11:23 am
Thanked: 15 times
GMAT Score:730

by prindaroy » Sat Sep 12, 2009 3:07 pm
The answer should be 60. The answer 10 is very silly. The total number of possibilities = 120 and in half of them, Bob will finish ahead of Marge. So the answer is 60. 10 cannot be the answer because there are 5 different people in 5 different positions.
Top
Post new topic Post Reply
• Page 1 of 1