DS2-4 : DS Archive
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# DS2-4

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SVP
Joined: 16 Oct 2003
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03 Jun 2004, 19:05
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Manager
Joined: 02 Jun 2004
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04 Jun 2004, 00:34
A.
1.apply recursively. sufficient
2.going in negative direction .does not mean all multiples of 5 are not in S.It is still a possibility but given info is not sufficient to infer anything.
SVP
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04 Jun 2004, 05:47
C it is. Can anyone enlighten us all.
Intern
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04 Jun 2004, 06:04
Here is my guess :

(1) tells us that 5 is in S thus recursively we have S={5,10...}

(2) tells us that 5 is in S so for the same reason S={5,0,-5...}

By combining (1) and (2) S contains all the multiple of 5 that is {0,5,10...}

What do u think guys ?
Manager
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04 Jun 2004, 12:27
I fell for the trap.C is correct.
S is a set of integers (not necessarily just positive integers).Question is "Is every multiple of 5 is in S?".
#1 misses negtive multiples (-5,-10...)
#2 misses positive multiples (5,10,...)
So,together covers all multiples.
That is the beauty of the DS questions.Small twist to a relatively easy question can differrentiate best people from the good.
SVP
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04 Jun 2004, 13:44
S is a set of integers and we do not know the number of elements in it.
Manager
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04 Jun 2004, 14:16
That is true but the question is "Is every multiple of 5 is in S?". 1 and 2 together guarantee that every multiple of 5 will be in S. S could still have other unrelated integers like 23,56,91,-43....but we dont care. Question is NOT "Is every element in S is multiple of 5?"

EDIT: wow, my title just got changed to manager.This is the quickest promotion I ever got in my life .Just took two days.
Intern
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05 Jun 2004, 04:03
GoalStanford wrote:
I fell for the trap.C is correct.
S is a set of integers (not necessarily just positive integers).Question is "Is every multiple of 5 is in S?".
#1 misses negtive multiples (-5,-10...)
#2 misses positive multiples (5,10,...)
So,together covers all multiples.
That is the beauty of the DS questions.Small twist to a relatively easy question can differrentiate best people from the good.

Actually, I'm not sure negatives are considrered as multiples. I thought that (2) brought that info but then I changed my mind and thought that (2) actually brings 0 which (1) does not.

Also, when reading the question again my heart is going to D (even if i know it's not the answer).

(1) No --> sufficient
(2) No --> sufficient.

05 Jun 2004, 04:03
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