if ? denotes an operation, what is the value of : DS Archive
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# if ? denotes an operation, what is the value of

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if ? denotes an operation, what is the value of [#permalink]

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30 Aug 2007, 20:06
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if △ denotes an operation, what is the value of (a△b) △c ?

(1) a △ b = 5
(2) 5 △ c = 3
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30 Aug 2007, 20:11
Amit05 wrote:
if △ denotes an operation, what is the value of (a△b) △c ?

(1) a △ b = 5
(2) 5 △ c = 3

Stmnt 1 : Insuff since we don't know what C is, one of BCE
Stmnt 2 : Insuff, So C or E

But combining those too we get the value as 3, so C.

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30 Aug 2007, 20:20
Amit05 wrote:
if △ denotes an operation, what is the value of (a△b) △c ?

(1) a △ b = 5
(2) 5 △ c = 3

Arrived at C. Although i worked the problem a bit more cause I thought C was too obvious of an answer.

S1: doesnt tell us anything about C. Can't distribute △ C w/o knowing wut the operation of a △ b is. a△ b could be a*b a+b a-b a^b a/b etc...

S2: obviously insuff. nothing about a△ b

I stick w/ C
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31 Aug 2007, 00:45
St1:
could be 2+3=5, 1*5 = 5, 5/1 = 5 or 6-1 = 5 etc. Insufficient.

St2:
Nothing about a and b. Insufficient.

Using both st1 and st2:
we know 5 △ c = 3 and a △ b = 5 so (a△b) △c = 3. Sufficient.

Ans C
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31 Aug 2007, 06:17
i at first thought this might be E..but the plugged some numbers and always get 3...

so C it is..
31 Aug 2007, 06:17
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