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Someone is trying to remember a phone number but cannot

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Manager
Joined: 11 Jan 2007
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Someone is trying to remember a phone number but cannot [#permalink]

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28 Jul 2007, 09:49
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

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
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cool

Director
Joined: 08 Feb 2007
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28 Jul 2007, 10:25
4!/2! or 12

4! since there are four numbers

2! since three is a repeat.
Manager
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28 Jul 2007, 10:29
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
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28 Jul 2007, 10:53
Clear C.

4!/2! = 24/2 = 12.
28 Jul 2007, 10:53
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