the following Saturday night

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sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Fri May 07, 2010 5:04 am

The organizers of a week-long fair have hired exactly five security guards to patrol the fairgrounds at night for the duration of the event. Exactly two guards are assigned to patrol the grounds every night, with no guard assigned consecutive nights. If the fair begins on a Monday, how many different pairs of guards will be available to patrol the fairgrounds on the following Saturday night?
(A) 2
(B) 3
(C) 5
(D) 6
(E) 7

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Source: Beat The GMAT — Problem Solving | Fri May 07, 2010 5:04 am

iamseer: Master | Next Rank: 500 Posts; Posts: 170; Joined: Wed Jun 10, 2009 5:59 am; Thanked: 13 times

by iamseer » Fri May 07, 2010 10:02 am

IMO B

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analyst218: Master | Next Rank: 500 Posts; Posts: 140; Joined: Fri Feb 05, 2010 2:43 pm; Thanked: 3 times; GMAT Score:720

by analyst218 » Fri May 07, 2010 10:12 am

sanju09 wrote:The organizers of a week-long fair have hired exactly five security guards to patrol the fairgrounds at night for the duration of the event. Exactly two guards are assigned to patrol the grounds every night, with no guard assigned consecutive nights. If the fair begins on a Monday, how many different pairs of guards will be available to patrol the fairgrounds on the following Saturday night?
(A) 2
(B) 3
(C) 5
(D) 6
(E) 7

+1 for B too.
every day starting tuesday you have 3 guards going for the two spots. combination 3C2=3

clock60: Legendary Member; Posts: 759; Joined: Mon Apr 26, 2010 10:15 amFollowed by: 3 members; Thanked: 85 times

by clock60 » Fri May 07, 2010 10:53 am

also got B
if x1,x2,x3,x4,x5 are persons for patrolling
say for monday the given pair is (x1,x2), then for the next day we have x3,x4,x5 from with we have 3C2=3 pairs (x3 x4, x3 x5, x4 x5), let it be x3 x4, and for the following day we have 3 persons to chose from x1,x2,x5 and again 3 pairs

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