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# Number System!!

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Senior Manager
Joined: 15 Feb 2011
Posts: 262
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Kudos [?]: 74 [0], given: 9

Number System!! [#permalink]  18 Aug 2011, 10:47
00:00

Difficulty:

25% (medium)

Question Stats:

89% (01:29) correct 11% (00:15) wrong based on 9 sessions
If x* y = xy – 2(x + y) for all integers x and y, then 2* ( – 3) =
(A) – 16
(B) – 11
(C) – 4
(D 4
(E) 16

how to quickly solve such questions?
[Reveal] Spoiler: OA
Director
Status:
Joined: 24 Jul 2011
Posts: 771
GMAT 1: 780 Q51 V48
GRE 1: 1540 Q800 V740
Followers: 96

Kudos [?]: 397 [0], given: 15

Re: Number System!! [#permalink]  18 Aug 2011, 10:55
The quickest (rather only) way is to apply the given formula:

2*(-3) = 2*(-3) - 2 (2 + (-3) ) = -6 +2 = -4

Option (C)
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Director
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
Posts: 649
Followers: 37

Kudos [?]: 486 [0], given: 39

Re: Number System!! [#permalink]  18 Aug 2011, 12:22
2*(-3) = -6 -2(2-3) = -6 - 4+6 = -4 Ans.
No other quickest way.
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Director
Joined: 01 Feb 2011
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Kudos [?]: 81 [0], given: 42

Re: Number System!! [#permalink]  18 Aug 2011, 19:30
as per the expression 2*-3 = -6-(2*(2-3)) =-4

Re: Number System!!   [#permalink] 18 Aug 2011, 19:30
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