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# Someone is trying to remember a phone number but cannot

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Manager
Joined: 11 Jan 2007
Posts: 202
Location: Bangkok
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Someone is trying to remember a phone number but cannot [#permalink]  28 Jul 2007, 08:49
14. Someone is trying to remember a phone number but cannot remember the whole number. He remembers 296-xxxx. He also remembers that the last 4 numbers must contain two 3 and a 8 and a 7. How many possible combinations are there?
A.8
B.10
C.12
D.15
E.18
_________________

cool

Director
Joined: 08 Feb 2007
Posts: 610
Location: New Haven, CT
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[#permalink]  28 Jul 2007, 09:25
4!/2! or 12

4! since there are four numbers

2! since three is a repeat.
Manager
Joined: 08 Jul 2007
Posts: 174
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Kudos [?]: 5 [0], given: 0

[#permalink]  28 Jul 2007, 09:29
C.

There are 4!=24 ways to arrange the four numbers without the "3 restriction". Because of of the "3 restriction", 1/2 of those arrangments are repeats. So there are 24/12=12 combinations.
Senior Manager
Joined: 04 Jun 2007
Posts: 348
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[#permalink]  28 Jul 2007, 09:53
Clear C.

4!/2! = 24/2 = 12.
[#permalink] 28 Jul 2007, 09:53
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# Someone is trying to remember a phone number but cannot

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