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# M02 Q31 (DS)

Author Message
Intern
Affiliations: Phi Theta Kappa, Dean's list, Chancelors list, Who's Who award, ASCPA
Joined: 16 May 2011
Posts: 25
WE 1: Tax
Followers: 1

Kudos [?]: 4 [0], given: 7

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29 Sep 2011, 06:22
A

A) 9+9 = 18, since those are the largest single digits, it's our only option.
B) xy = z/9 supports more than one answer. 99, 72, 63...etc
Manager
Affiliations: University of Tehran
Joined: 06 Feb 2011
Posts: 203
Location: Iran (Islamic Republic of)
Concentration: Marketing
Schools: BU
GMAT 1: 680 Q45 V38
GPA: 4
WE: Marketing (Retail)
Followers: 8

Kudos [?]: 35 [0], given: 57

### Show Tags

29 Sep 2011, 08:50
Hey guys,

Restate the stem as follows:

Is the unknown number one of 12 15 18 21 24 27 30 33 36 39 42 45 48 ???

Lets translate
stmt 1 to : (X+Y)/18= Integer
stmt 2 to: XY/9= Integer

Consider stmt one alone: The digits in none of the listed numbers add up to a number divisible by 18. Sum of digits of 48 and 39 both yield 12, which is too low. So the answer to the stem is definitely NO. Suff

Consider stmt two alone: 36 is divisible by 9 (Yes to the stem) and also 90 is divisible by 9 (No to the stem) => Insuf

Guys, don't bother with 0. I don't think that in such questions regarding digits and digit place, we can consider one digit -ive and another +ve. Do we have a SINGLE number such as 1-2 or 4-5 (Don't read it minus: It's a negative two-digit number with the sign before the second digit)? If you consider 0, you can make, e.g., -99, but since the question doesn't determine the order of digits, then you have to also accept existence of 9-9

If you are still reluctant, ok, maybe we can consider -ive or +ive in such question, too, but even then you have to write the positive number like 10X+Y and -ive number like -(10X+Y). Even in this case your -99 and 99 are in fact the same number b/c the -ive sign is irrelevant to our discussion of what X and Y are. What counts is that X and y are both 9 in both numbers, so they are the same numbers actually.

Am I clear or just lost in my faulty reasoning?
_________________

Ambition, Motivation and Determination: the three "tion"s that lead to PERFECTION.

World! Respect Iran and Iranians as they respect you! Leave the governments with their own.

Manager
Joined: 10 Jul 2011
Posts: 115
GMAT 1: 700 Q50 V34
GMAT 2: 710 Q50 V35
Followers: 3

Kudos [?]: 21 [0], given: 10

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29 Sep 2011, 10:04
The reasoning has been explained by others.

However, there are 2 doubts still floating around:
1. The '0' question
2. The negative number thing

As far as the point about zero is concerned, the question clearly states that it is a a two digit number. I don't think zero qualifies as a two digit number.

Regarding point 2 (the negative number thing), I think mathematicians will agree that negative numbers can be multiples, however, I think GMAT only considers positive numbers when problems related to multiples, factors etc. are designed.

Just to clarify the point regarding zero, zero is not the factor of any number, however, it can be the multiple of a number (if it is clearly stated that non-negative numbers are to be considered).

Consider 'Kudos' if you like my post.
Manager
Joined: 20 Nov 2010
Posts: 224
Followers: 4

Kudos [?]: 18 [0], given: 38

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29 Sep 2011, 21:05
Totally agree with the fact that in case of negative numbers one can't assign -ve to any one of the digits.
_________________

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
MGMAT 6 650 (51,31) on 31/8/11
MGMAT 1 670 (48,33) on 04/9/11
MGMAT 2 670 (47,34) on 07/9/11
MGMAT 3 680 (47,35) on 18/9/11
GMAT Prep1 680 ( 50, 31) on 10/11/11

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
CR notes
http://gmatclub.com/forum/massive-collection-of-verbal-questions-sc-rc-and-cr-106195.html#p832142
http://gmatclub.com/forum/1001-ds-questions-file-106193.html#p832133
http://gmatclub.com/forum/gmat-prep-critical-reasoning-collection-106783.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html
http://gmatclub.com/forum/how-to-get-6-0-awa-my-guide-64327.html?hilit=chineseburned

Manager
Joined: 25 May 2011
Posts: 157
Followers: 2

Kudos [?]: 56 [0], given: 71

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07 Nov 2011, 09:50
Sign of the number is something different from the digits. with 2 digits of "9" and "9", we can reach the numbers of "99" and "-99"

But, the question asks "is the two digit number less than 50?" ,and not "is the number less than 50"?
Plz notice the delicate difference between these 2 questions. the answer of the first question is just 99. but the answer of second question is 99 and -99

A

Last edited by shahideh on 07 Nov 2011, 09:51, edited 1 time in total.
Manager
Joined: 16 Sep 2010
Posts: 223
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Concentration: Finance, Real Estate
GMAT 1: 740 Q48 V42
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Kudos [?]: 100 [0], given: 2

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14 Nov 2011, 22:45
Agree with the logic above. 99 is the only one that fits thereby making the statement sufficient to answer, no.
Current Student
Joined: 07 Sep 2011
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GMAT 2: 720 Q49 V39
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Followers: 2

Kudos [?]: 35 [0], given: 13

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01 Oct 2012, 08:00
XY (one number, 2 digits) is divisble by 3.
Is XY < 50? This is a Y/N answer. If you can answer with a Y/N, sufficient.

1) sum of digits is a multiple of 18... No two digits can equal any multiple of 18 greater than 18. Therefore the sum of X and Y must equal 18. There are only 2 digits that do that.. 9 and 9. So XY=99. SUFFICIENT.

2) Products of digits is a multiple of 9...
9*1=9
1*9=9... i can stop here. one number is greater than 50, the other one is not. INSUFFICIENT.

Re: M02 Q31 (DS)   [#permalink] 01 Oct 2012, 08:00

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# M02 Q31 (DS)

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