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The image shows an office key holder where 8 different keys must be p

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The image shows an office key holder where 8 different keys must be p  [#permalink]

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New post 04 Feb 2019, 15:04
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A
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C
D
E

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  25% (medium)

Question Stats:

79% (01:30) correct 21% (01:36) wrong based on 28 sessions

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GMATH practice question (Quant Class 18)

The image shows an office key holder where 8 different keys must be placed (one key per square).
If the two main keys must be placed in the blue squares, in how many ways can all the keys be placed in the key holder?

(A) 360
(B) 720
(C) 1440
(D) 2880
(E) 4320

Source: https://gmath.net

Attachment:
04-Feb19-12u.gif
04-Feb19-12u.gif [ 2.68 KiB | Viewed 375 times ]

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Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net
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Re: The image shows an office key holder where 8 different keys must be p  [#permalink]

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New post 04 Feb 2019, 19:29
fskilnik wrote:
Image

GMATH practice question (Quant Class 18)

The image shows an office key holder where 8 different keys must be placed (one key per square).
If the two main keys must be placed in the blue squares, in how many ways can all the keys be placed in the key holder?

(A) 360
(B) 720
(C) 1440
(D) 2880
(E) 4320

Source: https://gmath.net


So the 8 keys are - 2 main and 6 others..
2main can be placed in 2! Ways
6 others can be placed in 6! ways

Total 2!*6!=2*720=1440

C
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Re: The image shows an office key holder where 8 different keys must be p  [#permalink]

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New post 05 Feb 2019, 03:47
2 main keys can be placed in 2! ways and 6 keys in 6! ways
so total
6!*2! = 1440
IMO C


fskilnik wrote:
Image

GMATH practice question (Quant Class 18)

The image shows an office key holder where 8 different keys must be placed (one key per square).
If the two main keys must be placed in the blue squares, in how many ways can all the keys be placed in the key holder?

(A) 360
(B) 720
(C) 1440
(D) 2880
(E) 4320

Source: https://gmath.net

Attachment:
04-Feb19-12u.gif
GMATH Teacher
User avatar
P
Status: GMATH founder
Joined: 12 Oct 2010
Posts: 935
Re: The image shows an office key holder where 8 different keys must be p  [#permalink]

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New post 05 Feb 2019, 06:30
fskilnik wrote:
Image

GMATH practice question (Quant Class 18)

The image shows an office key holder where 8 different keys must be placed (one key per square).
If the two main keys must be placed in the blue squares, in how many ways can all the keys be placed in the key holder?

(A) 360
(B) 720
(C) 1440
(D) 2880
(E) 4320

Source: https://gmath.net

Our "official solution" is identical to the other two posted above. (Thank you for your contributions!)

Here is our wording:

\(?\,\,\,:\,\,\,\# \,\,{\rm{8 - keys}}\,\,{\rm{placing}}\)

\(?\,\,\, = \,\,\,\underbrace {\,{P_2}\,}_{{\rm{main}}\,\,{\rm{keys}}} \cdot \underbrace {\,{P_6}\,}_{{\rm{other}}\,\,{\rm{keys}}}\,\,\, = \,\,\,2!\,\, \cdot 6! = 2 \cdot 720 = 1440\)


The correct answer is therefore (C).


We follow the notations and rationale taught in the GMATH method.

Regards,
Fabio.
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Fabio Skilnik :: GMATH method creator (Math for the GMAT)
Our high-level "quant" preparation starts here: https://gmath.net
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Re: The image shows an office key holder where 8 different keys must be p   [#permalink] 05 Feb 2019, 06:30
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