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# From a bunch of five keys, three particular keys have to be

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Manager
Joined: 18 Dec 2012
Posts: 96

Kudos [?]: 55 [0], given: 34

Location: India
Concentration: General Management, Strategy
GMAT 1: 660 Q49 V32
GMAT 2: 530 Q37 V25
GPA: 3.32
WE: Manufacturing and Production (Manufacturing)
From a bunch of five keys, three particular keys have to be [#permalink]

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13 Oct 2013, 01:31
1
This post was
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Difficulty:

25% (medium)

Question Stats:

73% (01:03) correct 27% (01:43) wrong based on 44 sessions

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From a bunch of five keys, three particular keys have to be used to open a combination lock, such that the second key can be used only after the first key and they third key can be used only after the second key. What are the chances of opening the lock in a random selection of three keys?

A. 1/20
B. 1/30
C. 1/60
D. 1/80
E. 1/120
[Reveal] Spoiler: OA

_________________

I'm telling this because you don't get it. You think you get it which is not the same as actually getting it. Get it?

Kudos [?]: 55 [0], given: 34

Math Expert
Joined: 02 Sep 2009
Posts: 41871

Kudos [?]: 128527 [1], given: 12180

Re: From a bunch of five keys, three particular keys have to be [#permalink]

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13 Oct 2013, 02:58
1
KUDOS
Expert's post
Qoofi wrote:
From a bunch of five keys, three particular keys have to be used to open a combination lock, such that the second key can be used only after the first key and they third key can be used only after the second key. What are the chances of opening the lock in a random selection of three keys?

A. 1/20
B. 1/30
C. 1/60
D. 1/80
E. 1/120

P = 1/5*1/4*1/3 = 1/60.

_________________

Kudos [?]: 128527 [1], given: 12180

Re: From a bunch of five keys, three particular keys have to be   [#permalink] 13 Oct 2013, 02:58
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